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	$60.89	10.142%	$67.0655	$67.07	$67.05	$67.10
Purchase #2	$208.33	12.141%	$233.6233	$233.62	$233.60	$233.60
Purchase #3	$127.88	7.560%	$137.5477	$137.55	$137.55	$137.50
Purchase #4	$242.75	9.301%	$265.3282	$265.33	$265.35	$265.30
Purchase #5	$96.91	8.236%	$104.8915	$104.89	$104.90	$104.90
Purchase #6	$13.84	4.415%	$14.451	$14.45	$14.45	$14.50
Purchase #7	$121.55	12.226%	$136.4107	$136.41	$136.40	$136.40
7 purchase totals =	$872.15		$959.3179	$959.32	$959.30	$959.30