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	$88.37	13.481%	$100.2832	$100.28	$100.30	$100.30
Purchase #2	$87.67	7.297%	$94.0673	$94.07	$94.05	$94.10
Purchase #3	$226.42	7.778%	$244.0309	$244.03	$244.05	$244.00
Purchase #4	$98.93	4.845%	$103.7232	$103.72	$103.70	$103.70
Purchase #5	$31.45	12.150%	$35.2712	$35.27	$35.25	$35.30
Purchase #6	$132.98	7.181%	$142.5293	$142.53	$142.55	$142.50
Purchase #7	$13.95	9.449%	$15.2681	$15.27	$15.25	$15.30
7 purchase totals =	$679.77		$735.1732	$735.17	$735.15	$735.20