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 $199.25   12.843%   $224.8397   $224.84   $224.85   $224.80  
  Purchase #2 $91.92   9.389%   $100.5504   $100.55   $100.55   $100.60  
  Purchase #3 $78.55   9.138%   $85.7279   $85.73   $85.75   $85.70  
  Purchase #4 $28.68   6.862%   $30.648   $30.65   $30.65   $30.60  
  Purchase #5 $139.98   11.705%   $156.3647   $156.36   $156.35   $156.40  
  Purchase #6 $59.83   4.684%   $62.6324   $62.63   $62.65   $62.60  
  Purchase #7 $204.70   10.502%   $226.1976   $226.20   $226.20   $226.20  
  7 purchase totals = $802.91       $886.9607   $886.96   $887.00   $886.90