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 $43.57   7.281%   $46.7423   $46.74   $46.75   $46.70  
  Purchase #2 $90.48   5.651%   $95.593   $95.59   $95.60   $95.60  
  Purchase #3 $232.85   9.498%   $254.9661   $254.97   $254.95   $255.00  
  Purchase #4 $246.63   4.141%   $256.8429   $256.84   $256.85   $256.80  
  Purchase #5 $130.48   12.399%   $146.6582   $146.66   $146.65   $146.70  
  Purchase #6 $108.71   4.302%   $113.3867   $113.39   $113.40   $113.40  
  Purchase #7 $17.45   7.666%   $18.7877   $18.79   $18.80   $18.80  
  7 purchase totals = $870.17       $932.9769   $932.98   $933.00   $933.00