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 $218.53   12.574%   $246.008   $246.01   $246.00   $246.00  
  Purchase #2 $52.96   4.276%   $55.2246   $55.22   $55.20   $55.20  
  Purchase #3 $27.53   6.777%   $29.3957   $29.40   $29.40   $29.40  
  Purchase #4 $68.78   10.746%   $76.1711   $76.17   $76.15   $76.20  
  Purchase #5 $225.63   12.308%   $253.4005   $253.40   $253.40   $253.40  
  Purchase #6 $7.50   3.838%   $7.7879   $7.79   $7.80   $7.80  
  Purchase #7 $201.56   5.819%   $213.2888   $213.29   $213.30   $213.30  
  7 purchase totals = $802.49       $881.2766   $881.28   $881.25   $881.30