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	$37.43	9.518%	$40.9926	$40.99	$41.00	$41.00
Purchase #2	$50.51	13.780%	$57.4703	$57.47	$57.45	$57.50
Purchase #3	$196.51	4.565%	$205.4807	$205.48	$205.50	$205.50
Purchase #4	$149.63	13.538%	$169.8869	$169.89	$169.90	$169.90
Purchase #5	$142.95	7.258%	$153.3253	$153.33	$153.35	$153.30
Purchase #6	$97.60	3.198%	$100.7212	$100.72	$100.70	$100.70
Purchase #7	$152.57	7.699%	$164.3164	$164.32	$164.30	$164.30
7 purchase totals =	$827.20		$892.1934	$892.20	$892.20	$892.20