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 $236.27   5.460%   $249.1703   $249.17   $249.15   $249.20  
  Purchase #2 $183.58   4.799%   $192.39   $192.39   $192.40   $192.40  
  Purchase #3 $16.27   9.239%   $17.7732   $17.77   $17.75   $17.80  
  Purchase #4 $196.95   8.244%   $213.1866   $213.19   $213.20   $213.20  
  Purchase #5 $85.73   13.616%   $97.403   $97.40   $97.40   $97.40  
  Purchase #6 $31.92   13.264%   $36.1539   $36.15   $36.15   $36.20  
  Purchase #7 $33.41   5.121%   $35.1209   $35.12   $35.10   $35.10  
  7 purchase totals = $784.13       $841.1979   $841.19   $841.15   $841.30