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	$150.62	10.103%	$165.8371	$165.84	$165.85	$165.80
Purchase #2	$223.72	13.106%	$253.0407	$253.04	$253.05	$253.00
Purchase #3	$29.60	9.253%	$32.3389	$32.34	$32.35	$32.30
Purchase #4	$73.98	3.847%	$76.826	$76.83	$76.85	$76.80
Purchase #5	$9.52	10.728%	$10.5413	$10.54	$10.55	$10.50
Purchase #6	$241.69	3.530%	$250.2217	$250.22	$250.20	$250.20
Purchase #7	$37.74	6.351%	$40.1369	$40.14	$40.15	$40.10
7 purchase totals =	$766.87		$828.9426	$828.95	$829.00	$828.70