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	$34.90	4.768%	$36.564	$36.56	$36.55	$36.60
Purchase #2	$244.92	11.267%	$272.5151	$272.52	$272.50	$272.50
Purchase #3	$206.29	11.422%	$229.8524	$229.85	$229.85	$229.90
Purchase #4	$250.59	13.405%	$284.1816	$284.18	$284.20	$284.20
Purchase #5	$154.29	8.624%	$167.596	$167.60	$167.60	$167.60
Purchase #6	$113.43	12.125%	$127.1834	$127.18	$127.20	$127.20
Purchase #7	$90.30	13.507%	$102.4968	$102.50	$102.50	$102.50
7 purchase totals =	$1,094.72		$1,220.3893	$1,220.39	$1,220.40	$1,220.50