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	$247.74	10.734%	$274.3324	$274.33	$274.35	$274.30
Purchase #2	$211.31	6.733%	$225.5375	$225.54	$225.55	$225.50
Purchase #3	$213.71	9.160%	$233.2858	$233.29	$233.30	$233.30
Purchase #4	$89.48	13.670%	$101.7119	$101.71	$101.70	$101.70
Purchase #5	$83.42	6.283%	$88.6613	$88.66	$88.65	$88.70
Purchase #6	$76.46	4.824%	$80.1484	$80.15	$80.15	$80.10
Purchase #7	$12.38	10.146%	$13.6361	$13.64	$13.65	$13.60
7 purchase totals =	$934.50		$1,017.3134	$1,017.32	$1,017.35	$1,017.20