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	$34.92	12.298%	$39.2145	$39.21	$39.20	$39.20
Purchase #2	$139.49	3.381%	$144.2062	$144.21	$144.20	$144.20
Purchase #3	$99.46	5.838%	$105.2665	$105.27	$105.25	$105.30
Purchase #4	$131.36	3.557%	$136.0325	$136.03	$136.05	$136.00
Purchase #5	$66.25	13.330%	$75.0811	$75.08	$75.10	$75.10
Purchase #6	$14.30	4.511%	$14.9451	$14.95	$14.95	$14.90
Purchase #7	$141.60	7.680%	$152.4749	$152.47	$152.45	$152.50
7 purchase totals =	$627.38		$667.2208	$667.22	$667.20	$667.20