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 $119.96   8.571%   $130.2418   $130.24   $130.25   $130.20  
  Purchase #2 $48.32   8.235%   $52.2992   $52.30   $52.30   $52.30  
  Purchase #3 $245.86   8.172%   $265.9517   $265.95   $265.95   $266.00  
  Purchase #4 $52.95   9.457%   $57.9575   $57.96   $57.95   $58.00  
  Purchase #5 $86.73   10.536%   $95.8679   $95.87   $95.85   $95.90  
  Purchase #6 $164.74   4.502%   $172.1566   $172.16   $172.15   $172.20  
  Purchase #7 $27.97   8.536%   $30.3575   $30.36   $30.35   $30.40  
  7 purchase totals = $746.53       $804.8322   $804.84   $804.80   $805.00