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	$231.30	10.523%	$255.6397	$255.64	$255.65	$255.60
Purchase #2	$98.45	5.853%	$104.2123	$104.21	$104.20	$104.20
Purchase #3	$147.57	3.627%	$152.9224	$152.92	$152.90	$152.90
Purchase #4	$26.51	7.771%	$28.5701	$28.57	$28.55	$28.60
Purchase #5	$235.42	7.777%	$253.7286	$253.73	$253.75	$253.70
Purchase #6	$202.89	11.332%	$225.8815	$225.88	$225.90	$225.90
Purchase #7	$74.89	13.523%	$85.0174	$85.02	$85.00	$85.00
7 purchase totals =	$1,017.03		$1,105.9720	$1,105.97	$1,105.95	$1,105.90