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 $241.88   7.395%   $259.767   $259.77   $259.75   $259.80  
  Purchase #2 $34.88   6.188%   $37.0384   $37.04   $37.05   $37.00  
  Purchase #3 $45.64   9.748%   $50.089   $50.09   $50.10   $50.10  
  Purchase #4 $92.61   4.176%   $96.4774   $96.48   $96.50   $96.50  
  Purchase #5 $124.41   10.480%   $137.4482   $137.45   $137.45   $137.40  
  Purchase #6 $25.83   8.527%   $28.0325   $28.03   $28.05   $28.00  
  Purchase #7 $146.43   3.195%   $151.1084   $151.11   $151.10   $151.10  
  7 purchase totals = $711.68       $759.9609   $759.97   $760.00   $759.90