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	$12.67	7.263%	$13.5902	$13.59	$13.60	$13.60
Purchase #2	$122.39	3.780%	$127.0163	$127.02	$127.00	$127.00
Purchase #3	$49.85	13.251%	$56.4556	$56.46	$56.45	$56.50
Purchase #4	$79.37	10.769%	$87.9174	$87.92	$87.90	$87.90
Purchase #5	$11.62	10.182%	$12.8031	$12.80	$12.80	$12.80
Purchase #6	$45.72	6.304%	$48.6022	$48.60	$48.60	$48.60
Purchase #7	$238.63	12.824%	$269.2319	$269.23	$269.25	$269.20
7 purchase totals =	$560.25		$615.6167	$615.62	$615.60	$615.60