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	$233.75	5.696%	$247.0644	$247.06	$247.05	$247.10
Purchase #2	$121.58	13.343%	$137.8024	$137.80	$137.80	$137.80
Purchase #3	$190.72	11.274%	$212.2218	$212.22	$212.20	$212.20
Purchase #4	$229.42	4.743%	$240.3014	$240.30	$240.30	$240.30
Purchase #5	$247.85	12.696%	$279.317	$279.32	$279.30	$279.30
Purchase #6	$50.51	7.461%	$54.2786	$54.28	$54.30	$54.30
Purchase #7	$118.32	10.663%	$130.9365	$130.94	$130.95	$130.90
7 purchase totals =	$1,192.15		$1,301.9221	$1,301.92	$1,301.90	$1,301.90