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	$21.72	12.768%	$24.4932	$24.49	$24.50	$24.50
Purchase #2	$169.47	9.243%	$185.1341	$185.13	$185.15	$185.10
Purchase #3	$176.54	10.420%	$194.9355	$194.94	$194.95	$194.90
Purchase #4	$167.91	13.820%	$191.1152	$191.12	$191.10	$191.10
Purchase #5	$87.46	3.327%	$90.3698	$90.37	$90.35	$90.40
Purchase #6	$241.41	9.309%	$263.8829	$263.88	$263.90	$263.90
Purchase #7	$14.57	13.128%	$16.4827	$16.48	$16.50	$16.50
7 purchase totals =	$879.08		$966.4134	$966.41	$966.45	$966.40