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	$60.38	12.816%	$68.1183	$68.12	$68.10	$68.10
Purchase #2	$55.40	9.191%	$60.4918	$60.49	$60.50	$60.50
Purchase #3	$99.53	4.261%	$103.771	$103.77	$103.75	$103.80
Purchase #4	$89.31	13.522%	$101.3865	$101.39	$101.40	$101.40
Purchase #5	$105.31	7.783%	$113.5063	$113.51	$113.50	$113.50
Purchase #6	$118.61	8.130%	$128.253	$128.25	$128.25	$128.30
Purchase #7	$40.91	4.413%	$42.7154	$42.72	$42.70	$42.70
7 purchase totals =	$569.45		$618.2423	$618.25	$618.20	$618.30