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 $61.97   11.763%   $69.2595   $69.26   $69.25   $69.30  
  Purchase #2 $57.36   8.791%   $62.4025   $62.40   $62.40   $62.40  
  Purchase #3 $171.99   13.632%   $195.4357   $195.44   $195.45   $195.40  
  Purchase #4 $239.27   11.674%   $267.2024   $267.20   $267.20   $267.20  
  Purchase #5 $67.63   5.681%   $71.4721   $71.47   $71.45   $71.50  
  Purchase #6 $231.68   11.295%   $257.8483   $257.85   $257.85   $257.80  
  Purchase #7 $18.36   7.452%   $19.7282   $19.73   $19.75   $19.70  
  7 purchase totals = $848.26       $943.3487   $943.35   $943.35   $943.30