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	$104.92	12.104%	$117.6195	$117.62	$117.60	$117.60
Purchase #2	$248.29	10.778%	$275.0507	$275.05	$275.05	$275.10
Purchase #3	$105.56	5.288%	$111.142	$111.14	$111.15	$111.10
Purchase #4	$36.94	4.458%	$38.5868	$38.59	$38.60	$38.60
Purchase #5	$132.58	6.547%	$141.26	$141.26	$141.25	$141.30
Purchase #6	$9.26	9.506%	$10.1403	$10.14	$10.15	$10.10
Purchase #7	$141.94	11.387%	$158.1027	$158.10	$158.10	$158.10
7 purchase totals =	$779.49		$851.9020	$851.90	$851.90	$851.90