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	$155.30	10.473%	$171.5646	$171.56	$171.55	$171.60
Purchase #2	$132.79	8.475%	$144.044	$144.04	$144.05	$144.00
Purchase #3	$233.76	9.204%	$255.2753	$255.28	$255.30	$255.30
Purchase #4	$42.46	6.283%	$45.1278	$45.13	$45.15	$45.10
Purchase #5	$26.66	7.685%	$28.7088	$28.71	$28.70	$28.70
Purchase #6	$37.66	11.337%	$41.9295	$41.93	$41.95	$41.90
Purchase #7	$230.55	4.312%	$240.4913	$240.49	$240.50	$240.50
7 purchase totals =	$859.18		$927.1413	$927.14	$927.20	$927.10