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	$83.81	6.249%	$89.0473	$89.05	$89.05	$89.00
Purchase #2	$69.35	7.813%	$74.7683	$74.77	$74.75	$74.80
Purchase #3	$7.51	9.397%	$8.2157	$8.22	$8.20	$8.20
Purchase #4	$87.58	4.191%	$91.2505	$91.25	$91.25	$91.30
Purchase #5	$39.41	8.245%	$42.6594	$42.66	$42.65	$42.70
Purchase #6	$99.99	11.145%	$111.1339	$111.13	$111.15	$111.10
Purchase #7	$133.71	10.517%	$147.7723	$147.77	$147.75	$147.80
7 purchase totals =	$521.36		$564.8474	$564.85	$564.80	$564.90