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 $67.54   12.606%   $76.0541   $76.05   $76.05   $76.10  
  Purchase #2 $118.35   9.425%   $129.5045   $129.50   $129.50   $129.50  
  Purchase #3 $209.37   4.430%   $218.6451   $218.65   $218.65   $218.60  
  Purchase #4 $172.54   7.491%   $185.465   $185.47   $185.45   $185.50  
  Purchase #5 $142.96   3.545%   $148.0279   $148.03   $148.05   $148.00  
  Purchase #6 $45.68   6.439%   $48.6213   $48.62   $48.60   $48.60  
  Purchase #7 $224.48   11.580%   $250.4748   $250.47   $250.45   $250.50  
  7 purchase totals = $980.92       $1,056.7927   $1,056.79   $1,056.75   $1,056.80