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	$156.71	9.508%	$171.61	$171.61	$171.60	$171.60
Purchase #2	$250.87	10.203%	$276.4663	$276.47	$276.45	$276.50
Purchase #3	$67.62	4.385%	$70.5851	$70.59	$70.60	$70.60
Purchase #4	$24.30	13.852%	$27.666	$27.67	$27.65	$27.70
Purchase #5	$108.46	3.152%	$111.8787	$111.88	$111.90	$111.90
Purchase #6	$67.26	9.585%	$73.7069	$73.71	$73.70	$73.70
Purchase #7	$29.28	4.139%	$30.4919	$30.49	$30.50	$30.50
7 purchase totals =	$704.50		$762.4049	$762.42	$762.40	$762.50