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	$130.71	5.346%	$137.6978	$137.70	$137.70	$137.70
Purchase #2	$132.90	13.428%	$150.7458	$150.75	$150.75	$150.70
Purchase #3	$114.84	3.469%	$118.8238	$118.82	$118.80	$118.80
Purchase #4	$83.90	9.590%	$91.946	$91.95	$91.95	$91.90
Purchase #5	$90.62	9.275%	$99.025	$99.03	$99.05	$99.00
Purchase #6	$145.68	9.353%	$159.3055	$159.31	$159.30	$159.30
Purchase #7	$48.30	11.538%	$53.8729	$53.87	$53.85	$53.90
7 purchase totals =	$746.95		$811.4168	$811.43	$811.40	$811.30