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	$81.55	11.247%	$90.7219	$90.72	$90.70	$90.70
Purchase #2	$10.81	7.461%	$11.6165	$11.62	$11.60	$11.60
Purchase #3	$187.51	4.457%	$195.8673	$195.87	$195.85	$195.90
Purchase #4	$233.70	6.422%	$248.7082	$248.71	$248.70	$248.70
Purchase #5	$57.85	11.493%	$64.4987	$64.50	$64.50	$64.50
Purchase #6	$62.67	7.370%	$67.2888	$67.29	$67.30	$67.30
Purchase #7	$127.90	10.741%	$141.6377	$141.64	$141.65	$141.60
7 purchase totals =	$761.99		$820.3391	$820.35	$820.30	$820.30