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	$96.57	3.120%	$99.583	$99.58	$99.60	$99.60
Purchase #2	$132.94	10.295%	$146.6262	$146.63	$146.65	$146.60
Purchase #3	$215.90	4.307%	$225.1988	$225.20	$225.20	$225.20
Purchase #4	$70.42	11.170%	$78.2859	$78.29	$78.30	$78.30
Purchase #5	$208.41	13.249%	$236.0222	$236.02	$236.00	$236.00
Purchase #6	$156.29	10.274%	$172.3472	$172.35	$172.35	$172.30
Purchase #7	$156.29	10.542%	$172.7661	$172.77	$172.75	$172.80
7 purchase totals =	$1,036.82		$1,130.8294	$1,130.84	$1,130.85	$1,130.80