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 $90.82   3.491%   $93.9905   $93.99   $94.00   $94.00  
  Purchase #2 $119.39   5.299%   $125.7165   $125.72   $125.70   $125.70  
  Purchase #3 $104.46   7.206%   $111.9874   $111.99   $112.00   $112.00  
  Purchase #4 $65.43   8.319%   $70.8731   $70.87   $70.85   $70.90  
  Purchase #5 $215.29   12.325%   $241.8245   $241.82   $241.80   $241.80  
  Purchase #6 $55.29   5.514%   $58.3387   $58.34   $58.35   $58.30  
  Purchase #7 $192.34   3.585%   $199.2354   $199.24   $199.25   $199.20  
  7 purchase totals = $843.02       $901.9661   $901.97   $901.95   $901.90