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 $60.69   13.191%   $68.6956   $68.70   $68.70   $68.70  
  Purchase #2 $188.26   3.543%   $194.9301   $194.93   $194.95   $194.90  
  Purchase #3 $178.33   13.680%   $202.7255   $202.73   $202.75   $202.70  
  Purchase #4 $172.36   13.455%   $195.551   $195.55   $195.55   $195.60  
  Purchase #5 $16.49   8.748%   $17.9325   $17.93   $17.95   $17.90  
  Purchase #6 $130.60   13.798%   $148.6202   $148.62   $148.60   $148.60  
  Purchase #7 $89.68   13.591%   $101.8684   $101.87   $101.85   $101.90  
  7 purchase totals = $836.41       $930.3233   $930.33   $930.35   $930.30