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	$29.67	10.382%	$32.7503	$32.75	$32.75	$32.80
Purchase #2	$32.36	9.662%	$35.4866	$35.49	$35.50	$35.50
Purchase #3	$134.50	3.810%	$139.6245	$139.62	$139.60	$139.60
Purchase #4	$219.89	10.729%	$243.482	$243.48	$243.50	$243.50
Purchase #5	$133.29	11.550%	$148.685	$148.69	$148.70	$148.70
Purchase #6	$233.55	9.441%	$255.5995	$255.60	$255.60	$255.60
Purchase #7	$111.28	12.160%	$124.8116	$124.81	$124.80	$124.80
7 purchase totals =	$894.54		$980.4395	$980.44	$980.45	$980.50