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	$121.83	7.669%	$131.1731	$131.17	$131.15	$131.20
Purchase #2	$108.28	8.341%	$117.3116	$117.31	$117.30	$117.30
Purchase #3	$131.37	4.400%	$137.1503	$137.15	$137.15	$137.20
Purchase #4	$216.74	10.180%	$238.8041	$238.80	$238.80	$238.80
Purchase #5	$86.52	13.601%	$98.2876	$98.29	$98.30	$98.30
Purchase #6	$63.49	13.459%	$72.0351	$72.04	$72.05	$72.00
Purchase #7	$111.32	4.412%	$116.2314	$116.23	$116.25	$116.20
7 purchase totals =	$839.55		$910.9932	$910.99	$911.00	$911.00