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 $182.86   11.201%   $203.3421   $203.34   $203.35   $203.30  
  Purchase #2 $167.70   4.586%   $175.3907   $175.39   $175.40   $175.40  
  Purchase #3 $169.31   3.687%   $175.5525   $175.55   $175.55   $175.60  
  Purchase #4 $26.47   11.346%   $29.4733   $29.47   $29.45   $29.50  
  Purchase #5 $112.64   4.130%   $117.292   $117.29   $117.30   $117.30  
  Purchase #6 $46.56   8.459%   $50.4985   $50.50   $50.50   $50.50  
  Purchase #7 $175.48   13.726%   $199.5664   $199.57   $199.55   $199.60  
  7 purchase totals = $881.02       $951.1155   $951.11   $951.10   $951.20