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	$86.82	5.136%	$91.2791	$91.28	$91.30	$91.30
Purchase #2	$94.92	10.621%	$105.0015	$105.00	$105.00	$105.00
Purchase #3	$44.56	12.852%	$50.2869	$50.29	$50.30	$50.30
Purchase #4	$90.43	8.588%	$98.1961	$98.20	$98.20	$98.20
Purchase #5	$78.38	6.592%	$83.5468	$83.55	$83.55	$83.50
Purchase #6	$74.63	8.631%	$81.0713	$81.07	$81.05	$81.10
Purchase #7	$54.36	9.619%	$59.5889	$59.59	$59.60	$59.60
7 purchase totals =	$524.10		$568.9706	$568.98	$569.00	$569.00