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	$138.65	6.341%	$147.4418	$147.44	$147.45	$147.40
Purchase #2	$249.61	6.768%	$266.5036	$266.50	$266.50	$266.50
Purchase #3	$165.48	12.147%	$185.5809	$185.58	$185.60	$185.60
Purchase #4	$165.94	11.191%	$184.5103	$184.51	$184.50	$184.50
Purchase #5	$54.29	5.344%	$57.1913	$57.19	$57.20	$57.20
Purchase #6	$77.54	13.536%	$88.0358	$88.04	$88.05	$88.00
Purchase #7	$48.64	10.167%	$53.5852	$53.59	$53.60	$53.60
7 purchase totals =	$900.15		$982.8489	$982.85	$982.90	$982.80