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	$187.93	12.634%	$211.6731	$211.67	$211.65	$211.70
Purchase #2	$29.32	6.248%	$31.1519	$31.15	$31.15	$31.20
Purchase #3	$111.58	11.508%	$124.4206	$124.42	$124.40	$124.40
Purchase #4	$157.69	6.130%	$167.3564	$167.36	$167.35	$167.40
Purchase #5	$128.52	12.874%	$145.0657	$145.07	$145.05	$145.10
Purchase #6	$83.46	8.415%	$90.4832	$90.48	$90.50	$90.50
Purchase #7	$35.46	10.370%	$39.1372	$39.14	$39.15	$39.10
7 purchase totals =	$733.96		$809.2881	$809.29	$809.25	$809.40