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	$88.93	13.153%	$100.627	$100.63	$100.65	$100.60
Purchase #2	$18.35	13.202%	$20.7726	$20.77	$20.75	$20.80
Purchase #3	$164.58	4.754%	$172.4041	$172.40	$172.40	$172.40
Purchase #4	$138.42	10.554%	$153.0288	$153.03	$153.05	$153.00
Purchase #5	$249.60	4.558%	$260.9768	$260.98	$261.00	$261.00
Purchase #6	$134.38	13.285%	$152.2324	$152.23	$152.25	$152.20
Purchase #7	$126.64	4.149%	$131.8943	$131.89	$131.90	$131.90
7 purchase totals =	$920.90		$991.9360	$991.93	$992.00	$991.90