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 $81.25   3.268%   $83.9053   $83.91   $83.90   $83.90  
  Purchase #2 $143.86   4.352%   $150.1208   $150.12   $150.10   $150.10  
  Purchase #3 $171.37   9.696%   $187.986   $187.99   $188.00   $188.00  
  Purchase #4 $136.42   7.733%   $146.9694   $146.97   $146.95   $147.00  
  Purchase #5 $132.68   10.769%   $146.9683   $146.97   $146.95   $147.00  
  Purchase #6 $239.98   3.330%   $247.9713   $247.97   $247.95   $248.00  
  Purchase #7 $237.76   10.198%   $262.0068   $262.01   $262.00   $262.00  
  7 purchase totals = $1,143.32       $1,225.9279   $1,225.94   $1,225.85   $1,226.00