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 $249.50   4.491%   $260.705   $260.71   $260.70   $260.70  
  Purchase #2 $31.42   13.783%   $35.7506   $35.75   $35.75   $35.80  
  Purchase #3 $72.67   3.793%   $75.4264   $75.43   $75.45   $75.40  
  Purchase #4 $41.54   5.355%   $43.7645   $43.76   $43.75   $43.80  
  Purchase #5 $104.34   11.374%   $116.2076   $116.21   $116.20   $116.20  
  Purchase #6 $192.52   6.872%   $205.75   $205.75   $205.75   $205.80  
  Purchase #7 $139.86   13.262%   $158.4082   $158.41   $158.40   $158.40  
  7 purchase totals = $831.85       $896.0123   $896.02   $896.00   $896.10