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	$29.26	6.312%	$31.1069	$31.11	$31.10	$31.10
Purchase #2	$50.38	13.707%	$57.2856	$57.29	$57.30	$57.30
Purchase #3	$132.30	9.229%	$144.51	$144.51	$144.50	$144.50
Purchase #4	$148.82	4.380%	$155.3383	$155.34	$155.35	$155.30
Purchase #5	$126.25	10.613%	$139.6489	$139.65	$139.65	$139.60
Purchase #6	$166.35	5.779%	$175.9634	$175.96	$175.95	$176.00
Purchase #7	$131.30	4.553%	$137.2781	$137.28	$137.30	$137.30
7 purchase totals =	$784.66		$841.1312	$841.14	$841.15	$841.10