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	$144.45	7.398%	$155.1364	$155.14	$155.15	$155.10
Purchase #2	$210.33	6.130%	$223.2232	$223.22	$223.20	$223.20
Purchase #3	$122.32	6.702%	$130.5179	$130.52	$130.50	$130.50
Purchase #4	$145.66	6.301%	$154.838	$154.84	$154.85	$154.80
Purchase #5	$167.81	11.169%	$186.5527	$186.55	$186.55	$186.60
Purchase #6	$107.67	3.400%	$111.3308	$111.33	$111.35	$111.30
Purchase #7	$123.79	4.640%	$129.5339	$129.53	$129.55	$129.50
7 purchase totals =	$1,022.03		$1,091.1329	$1,091.13	$1,091.15	$1,091.00