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 $51.58   5.129%   $54.2255   $54.23   $54.25   $54.20  
  Purchase #2 $221.48   6.721%   $236.3657   $236.37   $236.35   $236.40  
  Purchase #3 $35.45   4.389%   $37.0059   $37.01   $37.00   $37.00  
  Purchase #4 $224.59   13.355%   $254.584   $254.58   $254.60   $254.60  
  Purchase #5 $61.91   4.168%   $64.4904   $64.49   $64.50   $64.50  
  Purchase #6 $44.64   12.305%   $50.133   $50.13   $50.15   $50.10  
  Purchase #7 $240.89   6.741%   $257.1284   $257.13   $257.15   $257.10  
  7 purchase totals = $880.54       $953.9329   $953.94   $954.00   $953.90