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	$249.25	11.812%	$278.6914	$278.69	$278.70	$278.70
Purchase #2	$26.78	5.236%	$28.1822	$28.18	$28.20	$28.20
Purchase #3	$48.94	11.573%	$54.6038	$54.60	$54.60	$54.60
Purchase #4	$206.38	8.433%	$223.784	$223.78	$223.80	$223.80
Purchase #5	$87.34	3.117%	$90.0624	$90.06	$90.05	$90.10
Purchase #6	$124.28	10.394%	$137.1977	$137.20	$137.20	$137.20
Purchase #7	$233.30	4.831%	$244.5707	$244.57	$244.55	$244.60
7 purchase totals =	$976.27		$1,057.0922	$1,057.08	$1,057.10	$1,057.20