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	$131.89	4.784%	$138.1996	$138.20	$138.20	$138.20
Purchase #2	$16.30	6.629%	$17.3805	$17.38	$17.40	$17.40
Purchase #3	$145.89	8.503%	$158.295	$158.30	$158.30	$158.30
Purchase #4	$164.49	12.649%	$185.2963	$185.30	$185.30	$185.30
Purchase #5	$153.72	4.461%	$160.5774	$160.58	$160.60	$160.60
Purchase #6	$237.91	12.424%	$267.4679	$267.47	$267.45	$267.50
Purchase #7	$55.44	7.476%	$59.5847	$59.58	$59.60	$59.60
7 purchase totals =	$905.64		$986.8014	$986.81	$986.85	$986.90