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 $46.66   7.654%   $50.2314   $50.23   $50.25   $50.20  
  Purchase #2 $112.54   5.716%   $118.9728   $118.97   $118.95   $119.00  
  Purchase #3 $159.75   8.772%   $173.7633   $173.76   $173.75   $173.80  
  Purchase #4 $238.42   5.607%   $251.7882   $251.79   $251.80   $251.80  
  Purchase #5 $45.63   13.417%   $51.7522   $51.75   $51.75   $51.80  
  Purchase #6 $48.38   10.139%   $53.2852   $53.29   $53.30   $53.30  
  Purchase #7 $196.86   9.282%   $215.1325   $215.13   $215.15   $215.10  
  7 purchase totals = $848.24       $914.9256   $914.92   $914.95   $915.00