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 $106.73   8.772%   $116.0924   $116.09   $116.10   $116.10  
  Purchase #2 $171.32   11.763%   $191.4724   $191.47   $191.45   $191.50  
  Purchase #3 $216.40   9.394%   $236.7286   $236.73   $236.75   $236.70  
  Purchase #4 $37.80   8.657%   $41.0723   $41.07   $41.05   $41.10  
  Purchase #5 $15.26   6.223%   $16.2096   $16.21   $16.20   $16.20  
  Purchase #6 $67.90   12.203%   $76.1858   $76.19   $76.20   $76.20  
  Purchase #7 $235.87   8.447%   $255.7939   $255.79   $255.80   $255.80  
  7 purchase totals = $851.28       $933.5550   $933.55   $933.55   $933.60