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	$164.26	3.472%	$169.9631	$169.96	$169.95	$170.00
Purchase #2	$152.31	10.704%	$168.6133	$168.61	$168.60	$168.60
Purchase #3	$214.32	13.264%	$242.7474	$242.75	$242.75	$242.70
Purchase #4	$10.70	3.265%	$11.0494	$11.05	$11.05	$11.00
Purchase #5	$155.48	6.377%	$165.395	$165.40	$165.40	$165.40
Purchase #6	$37.55	10.612%	$41.5348	$41.53	$41.55	$41.50
Purchase #7	$98.27	13.573%	$111.6082	$111.61	$111.60	$111.60
7 purchase totals =	$832.89		$910.9112	$910.91	$910.90	$910.80