Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $217.65   12.484%   $244.8214   $244.82   $244.80   $244.80  
  Purchase #2 $98.78   12.138%   $110.7699   $110.77   $110.75   $110.80  
  Purchase #3 $119.79   11.164%   $133.1634   $133.16   $133.15   $133.20  
  Purchase #4 $117.93   5.533%   $124.4551   $124.46   $124.45   $124.50  
  Purchase #5 $225.38   11.243%   $250.7195   $250.72   $250.70   $250.70  
  Purchase #6 $124.54   13.576%   $141.4476   $141.45   $141.45   $141.40  
  Purchase #7 $247.35   6.417%   $263.2224   $263.22   $263.20   $263.20  
  7 purchase totals = $1,151.42       $1,268.5993   $1,268.60   $1,268.50   $1,268.60