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 $35.71   6.711%   $38.1065   $38.11   $38.10   $38.10  
  Purchase #2 $110.54   7.602%   $118.9433   $118.94   $118.95   $118.90  
  Purchase #3 $93.78   5.671%   $99.0983   $99.10   $99.10   $99.10  
  Purchase #4 $129.44   4.490%   $135.2519   $135.25   $135.25   $135.30  
  Purchase #5 $87.84   11.472%   $97.917   $97.92   $97.90   $97.90  
  Purchase #6 $141.88   12.273%   $159.2929   $159.29   $159.30   $159.30  
  Purchase #7 $112.54   3.590%   $116.5802   $116.58   $116.60   $116.60  
  7 purchase totals = $711.73       $765.1901   $765.19   $765.20   $765.20