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 $248.39   6.265%   $263.9516   $263.95   $263.95   $264.00  
  Purchase #2 $143.59   4.534%   $150.1004   $150.10   $150.10   $150.10  
  Purchase #3 $241.78   4.327%   $252.2418   $252.24   $252.25   $252.20  
  Purchase #4 $64.92   3.234%   $67.0195   $67.02   $67.00   $67.00  
  Purchase #5 $140.86   6.750%   $150.3681   $150.37   $150.35   $150.40  
  Purchase #6 $166.91   9.522%   $182.8032   $182.80   $182.80   $182.80  
  Purchase #7 $89.87   8.802%   $97.7804   $97.78   $97.80   $97.80  
  7 purchase totals = $1,096.32       $1,164.2650   $1,164.26   $1,164.25   $1,164.30