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 $67.77   11.763%   $75.7418   $75.74   $75.75   $75.70  
  Purchase #2 $50.63   13.260%   $57.3435   $57.34   $57.35   $57.30  
  Purchase #3 $247.83   8.577%   $269.0864   $269.09   $269.10   $269.10  
  Purchase #4 $48.98   4.781%   $51.3217   $51.32   $51.30   $51.30  
  Purchase #5 $8.41   4.277%   $8.7697   $8.77   $8.75   $8.80  
  Purchase #6 $213.68   4.818%   $223.9751   $223.98   $224.00   $224.00  
  Purchase #7 $60.99   9.766%   $66.9463   $66.95   $66.95   $66.90  
  7 purchase totals = $698.29       $753.1845   $753.19   $753.20   $753.10