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	$246.58	13.189%	$279.1014	$279.10	$279.10	$279.10
Purchase #2	$126.29	8.838%	$137.4515	$137.45	$137.45	$137.50
Purchase #3	$103.62	6.285%	$110.1325	$110.13	$110.15	$110.10
Purchase #4	$168.94	6.275%	$179.541	$179.54	$179.55	$179.50
Purchase #5	$146.77	12.578%	$165.2307	$165.23	$165.25	$165.20
Purchase #6	$230.95	7.224%	$247.6338	$247.63	$247.65	$247.60
Purchase #7	$122.67	11.291%	$136.5207	$136.52	$136.50	$136.50
7 purchase totals =	$1,145.82		$1,255.6116	$1,255.60	$1,255.65	$1,255.50