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 $129.97   12.494%   $146.2085   $146.21   $146.20   $146.20  
  Purchase #2 $158.95   11.485%   $177.2054   $177.21   $177.20   $177.20  
  Purchase #3 $68.38   8.129%   $73.9386   $73.94   $73.95   $73.90  
  Purchase #4 $194.86   10.177%   $214.6909   $214.69   $214.70   $214.70  
  Purchase #5 $45.39   13.408%   $51.4759   $51.48   $51.50   $51.50  
  Purchase #6 $100.98   10.865%   $111.9515   $111.95   $111.95   $112.00  
  Purchase #7 $178.54   4.602%   $186.7564   $186.76   $186.75   $186.80  
  7 purchase totals = $877.07       $962.2272   $962.24   $962.25   $962.30