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 $14.66   13.809%   $16.6844   $16.68   $16.70   $16.70  
  Purchase #2 $31.68   4.790%   $33.1975   $33.20   $33.20   $33.20  
  Purchase #3 $74.98   7.504%   $80.6065   $80.61   $80.60   $80.60  
  Purchase #4 $146.77   7.120%   $157.22   $157.22   $157.20   $157.20  
  Purchase #5 $116.63   7.452%   $125.3213   $125.32   $125.30   $125.30  
  Purchase #6 $195.96   13.603%   $222.6164   $222.62   $222.60   $222.60  
  Purchase #7 $217.74   5.621%   $229.9792   $229.98   $230.00   $230.00  
  7 purchase totals = $798.42       $865.6253   $865.63   $865.60   $865.60