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 $121.94   8.671%   $132.5134   $132.51   $132.50   $132.50  
  Purchase #2 $229.83   11.538%   $256.3478   $256.35   $256.35   $256.30  
  Purchase #3 $161.79   12.302%   $181.6934   $181.69   $181.70   $181.70  
  Purchase #4 $245.45   8.468%   $266.2347   $266.23   $266.25   $266.20  
  Purchase #5 $166.38   13.551%   $188.9262   $188.93   $188.95   $188.90  
  Purchase #6 $84.57   10.850%   $93.7458   $93.75   $93.75   $93.70  
  Purchase #7 $165.66   10.293%   $182.7114   $182.71   $182.70   $182.70  
  7 purchase totals = $1,175.62       $1,302.1727   $1,302.17   $1,302.20   $1,302.00