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 $182.64   12.531%   $205.5266   $205.53   $205.55   $205.50  
  Purchase #2 $63.78   11.166%   $70.9017   $70.90   $70.90   $70.90  
  Purchase #3 $103.39   8.625%   $112.3074   $112.31   $112.30   $112.30  
  Purchase #4 $217.63   12.156%   $244.0851   $244.09   $244.10   $244.10  
  Purchase #5 $222.76   10.867%   $246.9673   $246.97   $246.95   $247.00  
  Purchase #6 $237.84   12.780%   $268.236   $268.24   $268.25   $268.20  
  Purchase #7 $64.96   7.158%   $69.6098   $69.61   $69.60   $69.60  
  7 purchase totals = $1,093.00       $1,217.6339   $1,217.65   $1,217.65   $1,217.60