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	$112.46	10.788%	$124.5922	$124.59	$124.60	$124.60
Purchase #2	$127.29	7.320%	$136.6076	$136.61	$136.60	$136.60
Purchase #3	$117.36	3.450%	$121.4089	$121.41	$121.40	$121.40
Purchase #4	$205.28	12.838%	$231.6338	$231.63	$231.65	$231.60
Purchase #5	$113.43	9.201%	$123.8667	$123.87	$123.85	$123.90
Purchase #6	$37.78	11.624%	$42.1715	$42.17	$42.15	$42.20
Purchase #7	$48.59	9.547%	$53.2289	$53.23	$53.25	$53.20
7 purchase totals =	$762.19		$833.5096	$833.51	$833.50	$833.50