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	$50.37	10.785%	$55.8024	$55.80	$55.80	$55.80
Purchase #2	$96.82	7.129%	$103.7223	$103.72	$103.70	$103.70
Purchase #3	$146.82	13.456%	$166.5761	$166.58	$166.60	$166.60
Purchase #4	$24.42	12.801%	$27.546	$27.55	$27.55	$27.50
Purchase #5	$169.98	5.324%	$179.0297	$179.03	$179.05	$179.00
Purchase #6	$165.76	3.867%	$172.1699	$172.17	$172.15	$172.20
Purchase #7	$35.75	6.623%	$38.1177	$38.12	$38.10	$38.10
7 purchase totals =	$689.92		$742.9641	$742.97	$742.95	$742.90