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 $22.30   13.804%   $25.3783   $25.38   $25.40   $25.40  
  Purchase #2 $247.41   4.545%   $258.6548   $258.65   $258.65   $258.70  
  Purchase #3 $87.30   10.593%   $96.5477   $96.55   $96.55   $96.50  
  Purchase #4 $65.35   12.560%   $73.558   $73.56   $73.55   $73.60  
  Purchase #5 $100.46   3.788%   $104.2654   $104.27   $104.25   $104.30  
  Purchase #6 $165.26   10.437%   $182.5082   $182.51   $182.50   $182.50  
  Purchase #7 $208.86   5.756%   $220.882   $220.88   $220.90   $220.90  
  7 purchase totals = $896.94       $961.7944   $961.80   $961.80   $961.90