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	$125.75	10.147%	$138.5099	$138.51	$138.50	$138.50
Purchase #2	$89.99	12.112%	$100.8896	$100.89	$100.90	$100.90
Purchase #3	$195.76	9.413%	$214.1869	$214.19	$214.20	$214.20
Purchase #4	$195.59	4.810%	$204.9979	$205.00	$205.00	$205.00
Purchase #5	$150.32	9.871%	$165.1581	$165.16	$165.15	$165.20
Purchase #6	$183.89	9.103%	$200.6295	$200.63	$200.65	$200.60
Purchase #7	$49.31	10.206%	$54.3426	$54.34	$54.35	$54.30
7 purchase totals =	$990.61		$1,078.7145	$1,078.72	$1,078.75	$1,078.70