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	$42.50	4.557%	$44.4367	$44.44	$44.45	$44.40
Purchase #2	$244.92	13.145%	$277.1147	$277.11	$277.10	$277.10
Purchase #3	$83.55	8.272%	$90.4613	$90.46	$90.45	$90.50
Purchase #4	$30.85	5.202%	$32.4548	$32.45	$32.45	$32.50
Purchase #5	$63.95	10.661%	$70.7677	$70.77	$70.75	$70.80
Purchase #6	$137.27	11.808%	$153.4788	$153.48	$153.50	$153.50
Purchase #7	$157.28	10.476%	$173.7567	$173.76	$173.75	$173.80
7 purchase totals =	$760.32		$842.4707	$842.47	$842.45	$842.60