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	$223.91	13.834%	$254.8857	$254.89	$254.90	$254.90
Purchase #2	$111.75	13.794%	$127.1648	$127.16	$127.15	$127.20
Purchase #3	$162.27	11.812%	$181.4373	$181.44	$181.45	$181.40
Purchase #4	$242.67	8.800%	$264.025	$264.03	$264.05	$264.00
Purchase #5	$10.93	10.820%	$12.1126	$12.11	$12.10	$12.10
Purchase #6	$51.98	3.146%	$53.6153	$53.62	$53.60	$53.60
Purchase #7	$108.34	12.575%	$121.9638	$121.96	$121.95	$122.00
7 purchase totals =	$911.85		$1,015.2045	$1,015.21	$1,015.20	$1,015.20