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	$78.32	9.239%	$85.556	$85.56	$85.55	$85.60
Purchase #2	$40.30	12.558%	$45.3609	$45.36	$45.35	$45.40
Purchase #3	$47.47	8.730%	$51.6141	$51.61	$51.60	$51.60
Purchase #4	$180.33	13.406%	$204.505	$204.51	$204.50	$204.50
Purchase #5	$64.57	11.564%	$72.0369	$72.04	$72.05	$72.00
Purchase #6	$115.94	10.176%	$127.7381	$127.74	$127.75	$127.70
Purchase #7	$30.59	11.839%	$34.2116	$34.21	$34.20	$34.20
7 purchase totals =	$557.52		$621.0226	$621.03	$621.00	$621.00