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	$8.67	9.821%	$9.5215	$9.52	$9.50	$9.50
Purchase #2	$105.68	5.231%	$111.2081	$111.21	$111.20	$111.20
Purchase #3	$126.92	3.437%	$131.2822	$131.28	$131.30	$131.30
Purchase #4	$33.74	12.311%	$37.8937	$37.89	$37.90	$37.90
Purchase #5	$152.33	13.707%	$173.2099	$173.21	$173.20	$173.20
Purchase #6	$137.65	8.542%	$149.4081	$149.41	$149.40	$149.40
Purchase #7	$148.34	10.606%	$164.0729	$164.07	$164.05	$164.10
7 purchase totals =	$713.33		$776.5964	$776.59	$776.55	$776.60