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 $92.95   8.181%   $100.5542   $100.55   $100.55   $100.60  
  Purchase #2 $109.71   6.327%   $116.6514   $116.65   $116.65   $116.70  
  Purchase #3 $60.79   4.439%   $63.4885   $63.49   $63.50   $63.50  
  Purchase #4 $236.43   9.541%   $258.9878   $258.99   $259.00   $259.00  
  Purchase #5 $94.80   10.492%   $104.7464   $104.75   $104.75   $104.70  
  Purchase #6 $23.86   4.132%   $24.8459   $24.85   $24.85   $24.80  
  Purchase #7 $89.34   9.462%   $97.7934   $97.79   $97.80   $97.80  
  7 purchase totals = $707.88       $767.0676   $767.07   $767.10   $767.10