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	$164.78	5.204%	$173.3552	$173.36	$173.35	$173.40
Purchase #2	$153.42	4.176%	$159.8268	$159.83	$159.85	$159.80
Purchase #3	$147.66	8.626%	$160.3972	$160.40	$160.40	$160.40
Purchase #4	$96.48	6.311%	$102.5689	$102.57	$102.55	$102.60
Purchase #5	$238.89	13.616%	$271.4173	$271.42	$271.40	$271.40
Purchase #6	$27.28	13.698%	$31.0168	$31.02	$31.00	$31.00
Purchase #7	$76.50	7.483%	$82.2245	$82.22	$82.20	$82.20
7 purchase totals =	$905.01		$980.8067	$980.82	$980.75	$980.80