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	$36.84	9.588%	$40.3722	$40.37	$40.35	$40.40
Purchase #2	$247.53	8.493%	$268.5527	$268.55	$268.55	$268.60
Purchase #3	$135.95	7.583%	$146.2591	$146.26	$146.25	$146.30
Purchase #4	$39.95	12.672%	$45.0125	$45.01	$45.00	$45.00
Purchase #5	$172.55	10.476%	$190.6263	$190.63	$190.65	$190.60
Purchase #6	$106.62	4.580%	$111.5032	$111.50	$111.50	$111.50
Purchase #7	$234.53	7.142%	$251.2801	$251.28	$251.30	$251.30
7 purchase totals =	$973.97		$1,053.6061	$1,053.60	$1,053.60	$1,053.70