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 $164.57   12.370%   $184.9273   $184.93   $184.95   $184.90  
  Purchase #2 $181.41   13.158%   $205.2799   $205.28   $205.30   $205.30  
  Purchase #3 $97.28   12.777%   $109.7095   $109.71   $109.70   $109.70  
  Purchase #4 $34.82   7.389%   $37.3928   $37.39   $37.40   $37.40  
  Purchase #5 $104.59   5.656%   $110.5056   $110.51   $110.50   $110.50  
  Purchase #6 $125.26   10.758%   $138.7355   $138.74   $138.75   $138.70  
  Purchase #7 $88.84   8.177%   $96.1044   $96.10   $96.10   $96.10  
  7 purchase totals = $796.77       $882.6550   $882.66   $882.70   $882.60