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 $15.76   10.761%   $17.4559   $17.46   $17.45   $17.50  
  Purchase #2 $172.81   13.280%   $195.7592   $195.76   $195.75   $195.80  
  Purchase #3 $29.40   12.389%   $33.0424   $33.04   $33.05   $33.00  
  Purchase #4 $214.27   8.508%   $232.5001   $232.50   $232.50   $232.50  
  Purchase #5 $50.48   4.523%   $52.7632   $52.76   $52.75   $52.80  
  Purchase #6 $155.79   12.548%   $175.3385   $175.34   $175.35   $175.30  
  Purchase #7 $56.42   7.643%   $60.7322   $60.73   $60.75   $60.70  
  7 purchase totals = $694.93       $767.5915   $767.59   $767.60   $767.60