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 $39.82   11.798%   $44.518   $44.52   $44.50   $44.50  
  Purchase #2 $116.51   8.154%   $126.0102   $126.01   $126.00   $126.00  
  Purchase #3 $85.53   10.607%   $94.6022   $94.60   $94.60   $94.60  
  Purchase #4 $15.39   12.265%   $17.2776   $17.28   $17.30   $17.30  
  Purchase #5 $231.30   13.140%   $261.6928   $261.69   $261.70   $261.70  
  Purchase #6 $135.85   4.457%   $141.9048   $141.90   $141.90   $141.90  
  Purchase #7 $42.34   12.397%   $47.5889   $47.59   $47.60   $47.60  
  7 purchase totals = $666.74       $733.5945   $733.59   $733.60   $733.60