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 $194.53   7.520%   $209.1587   $209.16   $209.15   $209.20  
  Purchase #2 $67.97   8.325%   $73.6285   $73.63   $73.65   $73.60  
  Purchase #3 $233.97   11.145%   $260.046   $260.05   $260.05   $260.00  
  Purchase #4 $67.56   5.496%   $71.2731   $71.27   $71.25   $71.30  
  Purchase #5 $213.97   3.583%   $221.6365   $221.64   $221.65   $221.60  
  Purchase #6 $30.58   3.465%   $31.6396   $31.64   $31.65   $31.60  
  Purchase #7 $106.53   7.405%   $114.4185   $114.42   $114.40   $114.40  
  7 purchase totals = $915.11       $981.8009   $981.81   $981.80   $981.70