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	$120.84	9.497%	$132.3162	$132.32	$132.30	$132.30
Purchase #2	$53.88	10.832%	$59.7163	$59.72	$59.70	$59.70
Purchase #3	$250.78	10.166%	$276.2743	$276.27	$276.25	$276.30
Purchase #4	$233.71	12.203%	$262.2296	$262.23	$262.25	$262.20
Purchase #5	$141.86	6.485%	$151.0596	$151.06	$151.05	$151.10
Purchase #6	$103.45	7.500%	$111.2088	$111.21	$111.20	$111.20
Purchase #7	$64.52	13.774%	$73.407	$73.41	$73.40	$73.40
7 purchase totals =	$969.04		$1,066.2118	$1,066.22	$1,066.15	$1,066.20