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	$187.78	13.666%	$213.442	$213.44	$213.45	$213.40
Purchase #2	$16.90	6.327%	$17.9693	$17.97	$17.95	$18.00
Purchase #3	$154.27	8.278%	$167.0405	$167.04	$167.05	$167.00
Purchase #4	$152.53	13.149%	$172.5862	$172.59	$172.60	$172.60
Purchase #5	$10.37	8.403%	$11.2414	$11.24	$11.25	$11.20
Purchase #6	$127.66	13.480%	$144.8686	$144.87	$144.85	$144.90
Purchase #7	$55.26	3.381%	$57.1283	$57.13	$57.15	$57.10
7 purchase totals =	$704.77		$784.2763	$784.28	$784.30	$784.20