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	$132.42	8.202%	$143.2811	$143.28	$143.30	$143.30
Purchase #2	$36.92	5.119%	$38.8099	$38.81	$38.80	$38.80
Purchase #3	$35.39	6.169%	$37.5732	$37.57	$37.55	$37.60
Purchase #4	$59.40	10.138%	$65.422	$65.42	$65.40	$65.40
Purchase #5	$27.39	4.240%	$28.5513	$28.55	$28.55	$28.60
Purchase #6	$188.81	10.616%	$208.8541	$208.85	$208.85	$208.90
Purchase #7	$227.39	7.374%	$244.1577	$244.16	$244.15	$244.20
7 purchase totals =	$707.72		$766.6493	$766.64	$766.60	$766.80