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	$218.87	9.613%	$239.91	$239.91	$239.90	$239.90
Purchase #2	$148.51	10.760%	$164.4897	$164.49	$164.50	$164.50
Purchase #3	$241.78	8.751%	$262.9382	$262.94	$262.95	$262.90
Purchase #4	$95.70	4.272%	$99.7883	$99.79	$99.80	$99.80
Purchase #5	$184.76	5.333%	$194.6133	$194.61	$194.60	$194.60
Purchase #6	$211.68	13.811%	$240.9151	$240.92	$240.90	$240.90
Purchase #7	$18.28	12.873%	$20.6332	$20.63	$20.65	$20.60
7 purchase totals =	$1,119.58		$1,223.2878	$1,223.29	$1,223.30	$1,223.20