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	$202.45	4.343%	$211.2424	$211.24	$211.25	$211.20
Purchase #2	$152.61	13.130%	$172.6477	$172.65	$172.65	$172.60
Purchase #3	$238.44	13.482%	$270.5865	$270.59	$270.60	$270.60
Purchase #4	$63.62	5.423%	$67.0701	$67.07	$67.05	$67.10
Purchase #5	$18.95	6.698%	$20.2193	$20.22	$20.20	$20.20
Purchase #6	$75.51	9.244%	$82.4901	$82.49	$82.50	$82.50
Purchase #7	$164.82	7.163%	$176.6261	$176.63	$176.65	$176.60
7 purchase totals =	$916.40		$1,000.8822	$1,000.89	$1,000.90	$1,000.80