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 $246.96   11.136%   $274.4615   $274.46   $274.45   $274.50  
  Purchase #2 $30.95   13.707%   $35.1923   $35.19   $35.20   $35.20  
  Purchase #3 $229.44   11.443%   $255.6948   $255.69   $255.70   $255.70  
  Purchase #4 $143.67   3.706%   $148.9944   $148.99   $149.00   $149.00  
  Purchase #5 $153.81   10.643%   $170.18   $170.18   $170.20   $170.20  
  Purchase #6 $10.82   12.406%   $12.1623   $12.16   $12.15   $12.20  
  Purchase #7 $53.89   12.366%   $60.554   $60.55   $60.55   $60.60  
  7 purchase totals = $869.54       $957.2393   $957.22   $957.25   $957.40