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 $60.94   12.689%   $68.6727   $68.67   $68.65   $68.70  
  Purchase #2 $146.46   10.516%   $161.8617   $161.86   $161.85   $161.90  
  Purchase #3 $140.93   9.452%   $154.2507   $154.25   $154.25   $154.30  
  Purchase #4 $176.89   10.276%   $195.0672   $195.07   $195.05   $195.10  
  Purchase #5 $158.79   12.380%   $178.4482   $178.45   $178.45   $178.40  
  Purchase #6 $56.67   8.824%   $61.6706   $61.67   $61.65   $61.70  
  Purchase #7 $131.25   13.785%   $149.3428   $149.34   $149.35   $149.30  
  7 purchase totals = $871.93       $969.3139   $969.31   $969.25   $969.40