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 $67.76   13.293%   $76.7673   $76.77   $76.75   $76.80  
  Purchase #2 $151.56   12.136%   $169.9533   $169.95   $169.95   $170.00  
  Purchase #3 $78.92   8.516%   $85.6408   $85.64   $85.65   $85.60  
  Purchase #4 $150.29   9.477%   $164.533   $164.53   $164.55   $164.50  
  Purchase #5 $67.73   12.522%   $76.2112   $76.21   $76.20   $76.20  
  Purchase #6 $87.64   8.178%   $94.8072   $94.81   $94.80   $94.80  
  Purchase #7 $168.60   11.726%   $188.37   $188.37   $188.35   $188.40  
  7 purchase totals = $772.50       $856.2828   $856.28   $856.25   $856.30