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 $83.68   12.660%   $94.2739   $94.27   $94.25   $94.30  
  Purchase #2 $242.42   4.624%   $253.6295   $253.63   $253.65   $253.60  
  Purchase #3 $66.77   11.384%   $74.3711   $74.37   $74.35   $74.40  
  Purchase #4 $55.80   10.800%   $61.8264   $61.83   $61.85   $61.80  
  Purchase #5 $200.78   8.719%   $218.286   $218.29   $218.30   $218.30  
  Purchase #6 $40.99   8.275%   $44.3819   $44.38   $44.40   $44.40  
  Purchase #7 $55.43   11.681%   $61.9048   $61.90   $61.90   $61.90  
  7 purchase totals = $745.87       $808.6736   $808.67   $808.70   $808.70