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 $92.26   12.198%   $103.5139   $103.51   $103.50   $103.50  
  Purchase #2 $78.98   6.551%   $84.154   $84.15   $84.15   $84.20  
  Purchase #3 $27.70   8.853%   $30.1523   $30.15   $30.15   $30.20  
  Purchase #4 $55.46   13.259%   $62.8134   $62.81   $62.80   $62.80  
  Purchase #5 $95.62   11.539%   $106.6536   $106.65   $106.65   $106.70  
  Purchase #6 $133.56   5.539%   $140.9579   $140.96   $140.95   $141.00  
  Purchase #7 $166.93   9.389%   $182.6031   $182.60   $182.60   $182.60  
  7 purchase totals = $650.51       $710.8482   $710.83   $710.80   $711.00