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	$82.41	8.567%	$89.4701	$89.47	$89.45	$89.50
Purchase #2	$65.51	3.392%	$67.7321	$67.73	$67.75	$67.70
Purchase #3	$244.58	13.519%	$277.6448	$277.64	$277.65	$277.60
Purchase #4	$53.82	12.529%	$60.5631	$60.56	$60.55	$60.60
Purchase #5	$27.95	3.816%	$29.0166	$29.02	$29.00	$29.00
Purchase #6	$95.39	12.226%	$107.0524	$107.05	$107.05	$107.10
Purchase #7	$92.35	8.337%	$100.0492	$100.05	$100.05	$100.00
7 purchase totals =	$662.01		$731.5283	$731.52	$731.50	$731.50