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	$38.30	11.144%	$42.5682	$42.57	$42.55	$42.60
Purchase #2	$203.42	3.454%	$210.4461	$210.45	$210.45	$210.40
Purchase #3	$148.46	10.105%	$163.4619	$163.46	$163.45	$163.50
Purchase #4	$51.50	7.296%	$55.2574	$55.26	$55.25	$55.30
Purchase #5	$146.58	3.418%	$151.5901	$151.59	$151.60	$151.60
Purchase #6	$107.25	3.734%	$111.2547	$111.25	$111.25	$111.30
Purchase #7	$138.63	10.840%	$153.6575	$153.66	$153.65	$153.70
7 purchase totals =	$834.14		$888.2359	$888.24	$888.20	$888.40