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	$142.83	4.678%	$149.5116	$149.51	$149.50	$149.50
Purchase #2	$138.48	7.109%	$148.3245	$148.32	$148.30	$148.30
Purchase #3	$166.42	3.720%	$172.6108	$172.61	$172.60	$172.60
Purchase #4	$100.27	8.320%	$108.6125	$108.61	$108.60	$108.60
Purchase #5	$171.85	5.766%	$181.7589	$181.76	$181.75	$181.80
Purchase #6	$51.93	8.427%	$56.3061	$56.31	$56.30	$56.30
Purchase #7	$214.68	8.588%	$233.1167	$233.12	$233.10	$233.10
7 purchase totals =	$986.46		$1,050.2411	$1,050.24	$1,050.15	$1,050.20