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	$19.46	12.492%	$21.8909	$21.89	$21.90	$21.90
Purchase #2	$41.39	8.588%	$44.9446	$44.94	$44.95	$44.90
Purchase #3	$152.66	9.471%	$167.1184	$167.12	$167.10	$167.10
Purchase #4	$144.95	8.548%	$157.3403	$157.34	$157.35	$157.30
Purchase #5	$132.78	4.490%	$138.7418	$138.74	$138.75	$138.70
Purchase #6	$43.37	7.393%	$46.5763	$46.58	$46.60	$46.60
Purchase #7	$80.42	12.670%	$90.6092	$90.61	$90.60	$90.60
7 purchase totals =	$615.03		$667.2215	$667.22	$667.25	$667.10