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	$20.69	5.760%	$21.8817	$21.88	$21.90	$21.90
Purchase #2	$14.93	4.564%	$15.6114	$15.61	$15.60	$15.60
Purchase #3	$44.71	13.754%	$50.8594	$50.86	$50.85	$50.90
Purchase #4	$102.45	7.529%	$110.1635	$110.16	$110.15	$110.20
Purchase #5	$57.77	4.871%	$60.584	$60.58	$60.60	$60.60
Purchase #6	$60.42	8.117%	$65.3243	$65.32	$65.30	$65.30
Purchase #7	$189.89	3.621%	$196.7659	$196.77	$196.75	$196.80
7 purchase totals =	$490.86		$521.1902	$521.18	$521.15	$521.30