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 $57.97   11.401%   $64.5792   $64.58   $64.60   $64.60  
  Purchase #2 $162.54   10.111%   $178.9744   $178.97   $178.95   $179.00  
  Purchase #3 $166.47   10.145%   $183.3584   $183.36   $183.35   $183.40  
  Purchase #4 $140.62   11.338%   $156.5635   $156.56   $156.55   $156.60  
  Purchase #5 $87.84   5.790%   $92.9259   $92.93   $92.95   $92.90  
  Purchase #6 $125.77   9.535%   $137.7622   $137.76   $137.75   $137.80  
  Purchase #7 $146.39   5.603%   $154.5922   $154.59   $154.60   $154.60  
  7 purchase totals = $887.60       $968.7558   $968.75   $968.75   $968.90