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 $88.94   10.156%   $97.9727   $97.97   $97.95   $98.00  
  Purchase #2 $69.90   3.589%   $72.4087   $72.41   $72.40   $72.40  
  Purchase #3 $68.64   7.257%   $73.6212   $73.62   $73.60   $73.60  
  Purchase #4 $189.46   3.426%   $195.9509   $195.95   $195.95   $196.00  
  Purchase #5 $75.57   3.332%   $78.088   $78.09   $78.10   $78.10  
  Purchase #6 $61.49   3.389%   $63.5739   $63.57   $63.55   $63.60  
  Purchase #7 $234.67   11.344%   $261.291   $261.29   $261.30   $261.30  
  7 purchase totals = $788.67       $842.9064   $842.90   $842.85   $843.00