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	$218.45	12.645%	$246.073	$246.07	$246.05	$246.10
Purchase #2	$139.98	8.105%	$151.3254	$151.33	$151.35	$151.30
Purchase #3	$29.72	11.696%	$33.1961	$33.20	$33.20	$33.20
Purchase #4	$68.35	5.704%	$72.2487	$72.25	$72.25	$72.20
Purchase #5	$122.40	3.796%	$127.0463	$127.05	$127.05	$127.00
Purchase #6	$247.40	4.463%	$258.4415	$258.44	$258.45	$258.40
Purchase #7	$24.42	10.701%	$27.0332	$27.03	$27.05	$27.00
7 purchase totals =	$850.72		$915.3642	$915.37	$915.40	$915.20