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	$45.32	12.139%	$50.8214	$50.82	$50.80	$50.80
Purchase #2	$147.51	12.335%	$165.7054	$165.71	$165.70	$165.70
Purchase #3	$120.53	3.525%	$124.7787	$124.78	$124.80	$124.80
Purchase #4	$221.28	5.497%	$233.4438	$233.44	$233.45	$233.40
Purchase #5	$183.30	7.414%	$196.8899	$196.89	$196.90	$196.90
Purchase #6	$26.97	5.431%	$28.4347	$28.43	$28.45	$28.40
Purchase #7	$244.50	4.153%	$254.6541	$254.65	$254.65	$254.70
7 purchase totals =	$989.41		$1,054.7280	$1,054.72	$1,054.75	$1,054.70