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 $88.49   7.524%   $95.148   $95.15   $95.15   $95.10  
  Purchase #2 $229.82   8.369%   $249.0536   $249.05   $249.05   $249.10  
  Purchase #3 $125.80   4.696%   $131.7076   $131.71   $131.70   $131.70  
  Purchase #4 $79.98   3.856%   $83.064   $83.06   $83.05   $83.10  
  Purchase #5 $112.74   3.576%   $116.7716   $116.77   $116.75   $116.80  
  Purchase #6 $68.54   6.733%   $73.1548   $73.15   $73.15   $73.20  
  Purchase #7 $38.93   12.693%   $43.8714   $43.87   $43.85   $43.90  
  7 purchase totals = $744.30       $792.7710   $792.76   $792.70   $792.90