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 $151.26   3.822%   $157.0412   $157.04   $157.05   $157.00  
  Purchase #2 $169.67   13.836%   $193.1455   $193.15   $193.15   $193.10  
  Purchase #3 $25.59   10.122%   $28.1802   $28.18   $28.20   $28.20  
  Purchase #4 $224.34   7.831%   $241.9081   $241.91   $241.90   $241.90  
  Purchase #5 $83.88   12.422%   $94.2996   $94.30   $94.30   $94.30  
  Purchase #6 $204.88   4.595%   $214.2942   $214.29   $214.30   $214.30  
  Purchase #7 $46.56   4.651%   $48.7255   $48.73   $48.75   $48.70  
  7 purchase totals = $906.18       $977.5943   $977.60   $977.65   $977.50