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	$120.27	8.507%	$130.5014	$130.50	$130.50	$130.50
Purchase #2	$247.31	10.218%	$272.5801	$272.58	$272.60	$272.60
Purchase #3	$113.34	3.393%	$117.1856	$117.19	$117.20	$117.20
Purchase #4	$67.51	3.416%	$69.8161	$69.82	$69.80	$69.80
Purchase #5	$144.79	6.140%	$153.6801	$153.68	$153.70	$153.70
Purchase #6	$134.69	9.699%	$147.7536	$147.75	$147.75	$147.80
Purchase #7	$100.59	10.768%	$111.4215	$111.42	$111.40	$111.40
7 purchase totals =	$928.50		$1,002.9384	$1,002.94	$1,002.95	$1,003.00