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	$10.94	11.481%	$12.196	$12.20	$12.20	$12.20
Purchase #2	$119.55	8.535%	$129.7536	$129.75	$129.75	$129.80
Purchase #3	$186.68	7.592%	$200.8527	$200.85	$200.85	$200.90
Purchase #4	$117.41	11.212%	$130.574	$130.57	$130.55	$130.60
Purchase #5	$56.88	7.528%	$61.1619	$61.16	$61.15	$61.20
Purchase #6	$94.86	11.229%	$105.5118	$105.51	$105.50	$105.50
Purchase #7	$159.40	8.454%	$172.8757	$172.88	$172.90	$172.90
7 purchase totals =	$745.72		$812.9257	$812.92	$812.90	$813.10