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 $56.67   5.318%   $59.6837   $59.68   $59.70   $59.70  
  Purchase #2 $158.57   6.853%   $169.4368   $169.44   $169.45   $169.40  
  Purchase #3 $204.40   4.430%   $213.4549   $213.45   $213.45   $213.50  
  Purchase #4 $58.94   11.570%   $65.7594   $65.76   $65.75   $65.80  
  Purchase #5 $32.97   6.597%   $35.145   $35.15   $35.15   $35.10  
  Purchase #6 $135.93   13.772%   $154.6503   $154.65   $154.65   $154.70  
  Purchase #7 $15.95   11.159%   $17.7299   $17.73   $17.75   $17.70  
  7 purchase totals = $663.43       $715.8600   $715.86   $715.90   $715.90