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 $44.72   9.759%   $49.0842   $49.08   $49.10   $49.10  
  Purchase #2 $44.89   4.358%   $46.8463   $46.85   $46.85   $46.80  
  Purchase #3 $92.57   8.775%   $100.693   $100.69   $100.70   $100.70  
  Purchase #4 $86.75   7.399%   $93.1686   $93.17   $93.15   $93.20  
  Purchase #5 $213.84   6.455%   $227.6434   $227.64   $227.65   $227.60  
  Purchase #6 $199.98   9.758%   $219.494   $219.49   $219.50   $219.50  
  Purchase #7 $42.78   9.186%   $46.7098   $46.71   $46.70   $46.70  
  7 purchase totals = $725.53       $783.6393   $783.63   $783.65   $783.60