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	$238.34	11.295%	$265.2605	$265.26	$265.25	$265.30
Purchase #2	$127.46	13.717%	$144.9437	$144.94	$144.95	$144.90
Purchase #3	$83.79	8.332%	$90.7714	$90.77	$90.75	$90.80
Purchase #4	$107.40	11.610%	$119.8691	$119.87	$119.85	$119.90
Purchase #5	$105.83	5.225%	$111.3596	$111.36	$111.35	$111.40
Purchase #6	$142.57	6.209%	$151.4222	$151.42	$151.40	$151.40
Purchase #7	$14.83	12.846%	$16.7351	$16.74	$16.75	$16.70
7 purchase totals =	$820.22		$900.3616	$900.36	$900.30	$900.40