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	$34.60	10.172%	$38.1195	$38.12	$38.10	$38.10
Purchase #2	$158.29	9.222%	$172.8875	$172.89	$172.90	$172.90
Purchase #3	$63.94	3.237%	$66.0097	$66.01	$66.00	$66.00
Purchase #4	$11.38	7.830%	$12.2711	$12.27	$12.25	$12.30
Purchase #5	$87.41	5.576%	$92.284	$92.28	$92.30	$92.30
Purchase #6	$26.80	7.676%	$28.8572	$28.86	$28.85	$28.90
Purchase #7	$76.91	5.767%	$81.3454	$81.35	$81.35	$81.30
7 purchase totals =	$459.33		$491.7744	$491.78	$491.75	$491.80