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	$235.29	12.801%	$265.4095	$265.41	$265.40	$265.40
Purchase #2	$93.65	10.833%	$103.7951	$103.80	$103.80	$103.80
Purchase #3	$133.31	8.458%	$144.5854	$144.59	$144.60	$144.60
Purchase #4	$18.47	11.823%	$20.6537	$20.65	$20.65	$20.70
Purchase #5	$151.62	13.583%	$172.2145	$172.21	$172.20	$172.20
Purchase #6	$35.42	9.665%	$38.8433	$38.84	$38.85	$38.80
Purchase #7	$237.78	7.361%	$255.283	$255.28	$255.30	$255.30
7 purchase totals =	$905.54		$1,000.7845	$1,000.78	$1,000.80	$1,000.80