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	$20.64	5.200%	$21.7133	$21.71	$21.70	$21.70
Purchase #2	$204.85	5.744%	$216.6166	$216.62	$216.60	$216.60
Purchase #3	$241.47	5.298%	$254.2631	$254.26	$254.25	$254.30
Purchase #4	$213.31	7.168%	$228.6001	$228.60	$228.60	$228.60
Purchase #5	$48.29	10.417%	$53.3204	$53.32	$53.30	$53.30
Purchase #6	$69.89	11.775%	$78.1195	$78.12	$78.10	$78.10
Purchase #7	$111.88	7.339%	$120.0909	$120.09	$120.10	$120.10
7 purchase totals =	$910.33		$972.7239	$972.72	$972.65	$972.70