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	$133.35	13.512%	$151.3683	$151.37	$151.35	$151.40
Purchase #2	$250.26	8.826%	$272.3479	$272.35	$272.35	$272.30
Purchase #3	$169.28	13.114%	$191.4794	$191.48	$191.50	$191.50
Purchase #4	$91.84	4.103%	$95.6082	$95.61	$95.60	$95.60
Purchase #5	$107.89	4.378%	$112.6134	$112.61	$112.60	$112.60
Purchase #6	$238.47	3.594%	$247.0406	$247.04	$247.05	$247.00
Purchase #7	$145.85	12.469%	$164.036	$164.04	$164.05	$164.00
7 purchase totals =	$1,136.94		$1,234.4938	$1,234.50	$1,234.50	$1,234.40