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 $180.27   12.183%   $202.2323   $202.23   $202.25   $202.20  
  Purchase #2 $207.80   12.324%   $233.4093   $233.41   $233.40   $233.40  
  Purchase #3 $158.27   11.663%   $176.729   $176.73   $176.75   $176.70  
  Purchase #4 $176.97   9.403%   $193.6105   $193.61   $193.60   $193.60  
  Purchase #5 $10.63   10.489%   $11.745   $11.75   $11.75   $11.70  
  Purchase #6 $250.56   5.319%   $263.8873   $263.89   $263.90   $263.90  
  Purchase #7 $184.71   8.139%   $199.7435   $199.74   $199.75   $199.70  
  7 purchase totals = $1,169.21       $1,281.3569   $1,281.36   $1,281.40   $1,281.20