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	$133.35	9.579%	$146.1236	$146.12	$146.10	$146.10
Purchase #2	$43.39	5.387%	$45.7274	$45.73	$45.75	$45.70
Purchase #3	$138.34	12.454%	$155.5689	$155.57	$155.55	$155.60
Purchase #4	$168.64	10.103%	$185.6777	$185.68	$185.70	$185.70
Purchase #5	$62.60	13.149%	$70.8313	$70.83	$70.85	$70.80
Purchase #6	$175.95	9.414%	$192.5139	$192.51	$192.50	$192.50
Purchase #7	$110.49	6.670%	$117.8597	$117.86	$117.85	$117.90
7 purchase totals =	$832.76		$914.3025	$914.30	$914.30	$914.30