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 $53.78   13.691%   $61.143   $61.14   $61.15   $61.10  
  Purchase #2 $35.47   5.818%   $37.5336   $37.53   $37.55   $37.50  
  Purchase #3 $131.70   8.163%   $142.4507   $142.45   $142.45   $142.50  
  Purchase #4 $222.97   9.236%   $243.5635   $243.56   $243.55   $243.60  
  Purchase #5 $234.39   8.232%   $253.685   $253.69   $253.70   $253.70  
  Purchase #6 $112.31   11.652%   $125.3964   $125.40   $125.40   $125.40  
  Purchase #7 $116.47   11.569%   $129.9444   $129.94   $129.95   $129.90  
  7 purchase totals = $907.09       $993.7166   $993.71   $993.75   $993.70