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	$139.85	11.363%	$155.7412	$155.74	$155.75	$155.70
Purchase #2	$202.68	13.587%	$230.2181	$230.22	$230.20	$230.20
Purchase #3	$131.62	11.561%	$146.8366	$146.84	$146.85	$146.80
Purchase #4	$62.35	12.377%	$70.0671	$70.07	$70.05	$70.10
Purchase #5	$42.64	6.844%	$45.5583	$45.56	$45.55	$45.60
Purchase #6	$234.41	8.470%	$254.2645	$254.26	$254.25	$254.30
Purchase #7	$160.91	11.180%	$178.8997	$178.90	$178.90	$178.90
7 purchase totals =	$974.46		$1,081.5855	$1,081.59	$1,081.55	$1,081.60