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 $214.73   12.373%   $241.2985   $241.30   $241.30   $241.30  
  Purchase #2 $182.93   12.781%   $206.3103   $206.31   $206.30   $206.30  
  Purchase #3 $163.92   7.606%   $176.3878   $176.39   $176.40   $176.40  
  Purchase #4 $48.50   11.783%   $54.2148   $54.21   $54.20   $54.20  
  Purchase #5 $34.43   3.446%   $35.6165   $35.62   $35.60   $35.60  
  Purchase #6 $140.32   7.612%   $151.0012   $151.00   $151.00   $151.00  
  Purchase #7 $65.33   4.821%   $68.4796   $68.48   $68.50   $68.50  
  7 purchase totals = $850.16       $933.3087   $933.31   $933.30   $933.30