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	$74.36	4.865%	$77.9776	$77.98	$78.00	$78.00
Purchase #2	$116.26	4.514%	$121.508	$121.51	$121.50	$121.50
Purchase #3	$111.29	8.246%	$120.467	$120.47	$120.45	$120.50
Purchase #4	$90.77	3.712%	$94.1394	$94.14	$94.15	$94.10
Purchase #5	$81.39	12.564%	$91.6158	$91.62	$91.60	$91.60
Purchase #6	$30.92	4.196%	$32.2174	$32.22	$32.20	$32.20
Purchase #7	$153.56	13.680%	$174.567	$174.57	$174.55	$174.60
7 purchase totals =	$658.55		$712.4922	$712.51	$712.45	$712.50