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	$37.30	13.169%	$42.212	$42.21	$42.20	$42.20
Purchase #2	$217.43	9.172%	$237.3727	$237.37	$237.35	$237.40
Purchase #3	$149.43	6.179%	$158.6633	$158.66	$158.65	$158.70
Purchase #4	$22.50	11.300%	$25.0425	$25.04	$25.05	$25.00
Purchase #5	$138.47	5.864%	$146.5899	$146.59	$146.60	$146.60
Purchase #6	$18.30	7.774%	$19.7226	$19.72	$19.70	$19.70
Purchase #7	$157.98	5.666%	$166.9311	$166.93	$166.95	$166.90
7 purchase totals =	$741.41		$796.5341	$796.52	$796.50	$796.50