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	$91.39	12.585%	$102.8914	$102.89	$102.90	$102.90
Purchase #2	$248.82	6.377%	$264.6873	$264.69	$264.70	$264.70
Purchase #3	$146.36	4.687%	$153.2199	$153.22	$153.20	$153.20
Purchase #4	$130.35	8.245%	$141.0974	$141.10	$141.10	$141.10
Purchase #5	$82.26	9.256%	$89.874	$89.87	$89.85	$89.90
Purchase #6	$193.25	13.633%	$219.5958	$219.60	$219.60	$219.60
Purchase #7	$233.52	8.123%	$252.4888	$252.49	$252.50	$252.50
7 purchase totals =	$1,125.95		$1,223.8546	$1,223.86	$1,223.85	$1,223.90