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	$11.77	11.677%	$13.1444	$13.14	$13.15	$13.10
Purchase #2	$101.36	3.787%	$105.1985	$105.20	$105.20	$105.20
Purchase #3	$56.36	8.442%	$61.1179	$61.12	$61.10	$61.10
Purchase #4	$81.99	13.304%	$92.8979	$92.90	$92.90	$92.90
Purchase #5	$15.80	4.136%	$16.4535	$16.45	$16.45	$16.50
Purchase #6	$57.55	13.339%	$65.2266	$65.23	$65.25	$65.20
Purchase #7	$144.46	5.762%	$152.7838	$152.78	$152.80	$152.80
7 purchase totals =	$469.29		$506.8226	$506.82	$506.85	$506.80