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	$129.36	6.404%	$137.6442	$137.64	$137.65	$137.60
Purchase #2	$176.52	11.809%	$197.3652	$197.37	$197.35	$197.40
Purchase #3	$242.38	13.643%	$275.4479	$275.45	$275.45	$275.40
Purchase #4	$67.40	7.460%	$72.428	$72.43	$72.45	$72.40
Purchase #5	$132.30	10.140%	$145.7152	$145.72	$145.70	$145.70
Purchase #6	$113.62	9.411%	$124.3128	$124.31	$124.30	$124.30
Purchase #7	$99.44	11.799%	$111.1729	$111.17	$111.15	$111.20
7 purchase totals =	$961.02		$1,064.0862	$1,064.09	$1,064.05	$1,064.00