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 $113.56   11.787%   $126.9453   $126.95   $126.95   $126.90  
  Purchase #2 $175.83   5.325%   $185.1929   $185.19   $185.20   $185.20  
  Purchase #3 $187.27   12.147%   $210.0177   $210.02   $210.00   $210.00  
  Purchase #4 $7.25   9.451%   $7.9352   $7.94   $7.95   $7.90  
  Purchase #5 $54.90   9.573%   $60.1556   $60.16   $60.15   $60.20  
  Purchase #6 $195.61   11.703%   $218.5022   $218.50   $218.50   $218.50  
  Purchase #7 $13.92   9.622%   $15.2594   $15.26   $15.25   $15.30  
  7 purchase totals = $748.34       $824.0083   $824.02   $824.00   $824.00