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 $190.90   10.362%   $210.6811   $210.68   $210.70   $210.70  
  Purchase #2 $155.29   13.130%   $175.6796   $175.68   $175.70   $175.70  
  Purchase #3 $27.56   3.230%   $28.4502   $28.45   $28.45   $28.50  
  Purchase #4 $112.31   7.149%   $120.339   $120.34   $120.35   $120.30  
  Purchase #5 $169.35   10.102%   $186.4577   $186.46   $186.45   $186.50  
  Purchase #6 $101.66   8.105%   $109.8995   $109.90   $109.90   $109.90  
  Purchase #7 $130.53   3.303%   $134.8414   $134.84   $134.85   $134.80  
  7 purchase totals = $887.60       $966.3485   $966.35   $966.40   $966.40