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 $242.37   8.754%   $263.5871   $263.59   $263.60   $263.60  
  Purchase #2 $133.95   10.527%   $148.0509   $148.05   $148.05   $148.10  
  Purchase #3 $122.99   4.216%   $128.1753   $128.18   $128.20   $128.20  
  Purchase #4 $28.32   9.163%   $30.915   $30.92   $30.90   $30.90  
  Purchase #5 $120.48   3.432%   $124.6149   $124.61   $124.60   $124.60  
  Purchase #6 $32.56   4.181%   $33.9213   $33.92   $33.90   $33.90  
  Purchase #7 $24.34   9.223%   $26.5849   $26.58   $26.60   $26.60  
  7 purchase totals = $705.01       $755.8494   $755.85   $755.85   $755.90