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	$62.92	5.630%	$66.4624	$66.46	$66.45	$66.50
Purchase #2	$16.86	10.773%	$18.6763	$18.68	$18.70	$18.70
Purchase #3	$141.29	8.615%	$153.4621	$153.46	$153.45	$153.50
Purchase #4	$50.71	7.665%	$54.5969	$54.60	$54.60	$54.60
Purchase #5	$96.47	7.731%	$103.9281	$103.93	$103.95	$103.90
Purchase #6	$39.53	13.593%	$44.9033	$44.90	$44.90	$44.90
Purchase #7	$136.41	9.417%	$149.2557	$149.26	$149.25	$149.30
7 purchase totals =	$544.19		$591.2848	$591.29	$591.30	$591.40