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	$11.62	4.829%	$12.1811	$12.18	$12.20	$12.20
Purchase #2	$31.90	11.563%	$35.5886	$35.59	$35.60	$35.60
Purchase #3	$66.29	12.594%	$74.6386	$74.64	$74.65	$74.60
Purchase #4	$96.60	7.189%	$103.5446	$103.54	$103.55	$103.50
Purchase #5	$109.98	5.561%	$116.096	$116.10	$116.10	$116.10
Purchase #6	$86.35	11.827%	$96.5626	$96.56	$96.55	$96.60
Purchase #7	$58.98	6.482%	$62.8031	$62.80	$62.80	$62.80
7 purchase totals =	$461.72		$501.4146	$501.41	$501.45	$501.40