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 $133.61   8.191%   $144.554   $144.55   $144.55   $144.60  
  Purchase #2 $118.95   5.796%   $125.8443   $125.84   $125.85   $125.80  
  Purchase #3 $96.93   9.842%   $106.4699   $106.47   $106.45   $106.50  
  Purchase #4 $69.44   9.857%   $76.2847   $76.28   $76.30   $76.30  
  Purchase #5 $176.77   13.147%   $200.01   $200.01   $200.00   $200.00  
  Purchase #6 $117.87   7.108%   $126.2482   $126.25   $126.25   $126.20  
  Purchase #7 $38.67   10.321%   $42.6611   $42.66   $42.65   $42.70  
  7 purchase totals = $752.24       $822.0722   $822.06   $822.05   $822.10