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	$230.72	4.682%	$241.5223	$241.52	$241.50	$241.50
Purchase #2	$33.84	12.800%	$38.1715	$38.17	$38.15	$38.20
Purchase #3	$212.74	13.272%	$240.9749	$240.97	$240.95	$241.00
Purchase #4	$90.89	10.733%	$100.6452	$100.65	$100.65	$100.60
Purchase #5	$130.42	3.462%	$134.9351	$134.94	$134.95	$134.90
Purchase #6	$65.61	8.624%	$71.2682	$71.27	$71.25	$71.30
Purchase #7	$176.56	7.666%	$190.0951	$190.10	$190.10	$190.10
7 purchase totals =	$940.78		$1,017.6123	$1,017.62	$1,017.55	$1,017.60