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	$131.25	6.326%	$139.5529	$139.55	$139.55	$139.60
Purchase #2	$185.64	3.242%	$191.6584	$191.66	$191.65	$191.70
Purchase #3	$246.62	7.148%	$264.2484	$264.25	$264.25	$264.20
Purchase #4	$9.58	12.388%	$10.7668	$10.77	$10.75	$10.80
Purchase #5	$94.75	10.222%	$104.4353	$104.44	$104.45	$104.40
Purchase #6	$103.83	7.821%	$111.9505	$111.95	$111.95	$112.00
Purchase #7	$39.92	7.205%	$42.7962	$42.80	$42.80	$42.80
7 purchase totals =	$811.59		$865.4085	$865.42	$865.40	$865.50