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 $67.42   12.506%   $75.8515   $75.85   $75.85   $75.90  
  Purchase #2 $173.75   12.546%   $195.5487   $195.55   $195.55   $195.50  
  Purchase #3 $216.91   12.136%   $243.2342   $243.23   $243.25   $243.20  
  Purchase #4 $51.43   12.372%   $57.7929   $57.79   $57.80   $57.80  
  Purchase #5 $108.63   3.866%   $112.8296   $112.83   $112.85   $112.80  
  Purchase #6 $240.80   8.361%   $260.9333   $260.93   $260.95   $260.90  
  Purchase #7 $24.92   11.193%   $27.7093   $27.71   $27.70   $27.70  
  7 purchase totals = $883.86       $973.8995   $973.89   $973.95   $973.80