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	$37.57	12.361%	$42.214	$42.21	$42.20	$42.20
Purchase #2	$159.63	4.530%	$166.8612	$166.86	$166.85	$166.90
Purchase #3	$156.53	10.707%	$173.2897	$173.29	$173.30	$173.30
Purchase #4	$96.83	3.719%	$100.4311	$100.43	$100.45	$100.40
Purchase #5	$22.48	10.188%	$24.7703	$24.77	$24.75	$24.80
Purchase #6	$137.43	5.207%	$144.586	$144.59	$144.60	$144.60
Purchase #7	$180.44	11.137%	$200.5356	$200.54	$200.55	$200.50
7 purchase totals =	$790.91		$852.6879	$852.69	$852.70	$852.70