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	$238.89	5.687%	$252.4757	$252.48	$252.50	$252.50
Purchase #2	$172.72	11.111%	$191.9109	$191.91	$191.90	$191.90
Purchase #3	$134.35	4.121%	$139.8866	$139.89	$139.90	$139.90
Purchase #4	$148.73	10.598%	$164.4924	$164.49	$164.50	$164.50
Purchase #5	$139.48	8.832%	$151.7989	$151.80	$151.80	$151.80
Purchase #6	$208.88	3.788%	$216.7924	$216.79	$216.80	$216.80
Purchase #7	$212.88	13.309%	$241.2122	$241.21	$241.20	$241.20
7 purchase totals =	$1,255.93		$1,358.5691	$1,358.57	$1,358.60	$1,358.60