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	$225.53	11.141%	$250.6563	$250.66	$250.65	$250.70
Purchase #2	$111.59	4.588%	$116.7097	$116.71	$116.70	$116.70
Purchase #3	$77.87	3.724%	$80.7699	$80.77	$80.75	$80.80
Purchase #4	$143.52	10.428%	$158.4863	$158.49	$158.50	$158.50
Purchase #5	$99.31	5.871%	$105.1405	$105.14	$105.15	$105.10
Purchase #6	$93.91	13.384%	$106.4789	$106.48	$106.50	$106.50
Purchase #7	$48.82	9.288%	$53.3544	$53.35	$53.35	$53.40
7 purchase totals =	$800.55		$871.5960	$871.60	$871.60	$871.70