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	$24.85	7.103%	$26.6151	$26.62	$26.60	$26.60
Purchase #2	$151.83	13.571%	$172.4348	$172.43	$172.45	$172.40
Purchase #3	$145.54	5.109%	$152.9756	$152.98	$153.00	$153.00
Purchase #4	$162.93	9.686%	$178.7114	$178.71	$178.70	$178.70
Purchase #5	$175.26	5.838%	$185.4917	$185.49	$185.50	$185.50
Purchase #6	$208.85	8.191%	$225.9569	$225.96	$225.95	$226.00
Purchase #7	$33.60	12.733%	$37.8783	$37.88	$37.90	$37.90
7 purchase totals =	$902.86		$980.0638	$980.07	$980.10	$980.10