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	$172.37	3.712%	$178.7684	$178.77	$178.75	$178.80
Purchase #2	$242.87	5.343%	$255.8465	$255.85	$255.85	$255.80
Purchase #3	$64.86	8.281%	$70.2311	$70.23	$70.25	$70.20
Purchase #4	$233.28	5.788%	$246.7822	$246.78	$246.80	$246.80
Purchase #5	$109.77	13.524%	$124.6153	$124.62	$124.60	$124.60
Purchase #6	$200.76	10.685%	$222.2112	$222.21	$222.20	$222.20
Purchase #7	$229.90	3.561%	$238.0867	$238.09	$238.10	$238.10
7 purchase totals =	$1,253.81		$1,336.5414	$1,336.55	$1,336.55	$1,336.50