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 $109.54   6.467%   $116.624   $116.62   $116.60   $116.60  
  Purchase #2 $116.86   7.231%   $125.3101   $125.31   $125.30   $125.30  
  Purchase #3 $57.67   8.657%   $62.6625   $62.66   $62.65   $62.70  
  Purchase #4 $25.92   8.118%   $28.0242   $28.02   $28.00   $28.00  
  Purchase #5 $162.37   12.669%   $182.9407   $182.94   $182.95   $182.90  
  Purchase #6 $157.84   3.191%   $162.8767   $162.88   $162.90   $162.90  
  Purchase #7 $127.47   7.172%   $136.6121   $136.61   $136.60   $136.60  
  7 purchase totals = $757.67       $815.0503   $815.04   $815.00   $815.00