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	$15.91	3.365%	$16.4454	$16.45	$16.45	$16.40
Purchase #2	$222.75	3.156%	$229.78	$229.78	$229.80	$229.80
Purchase #3	$82.77	9.115%	$90.3145	$90.31	$90.30	$90.30
Purchase #4	$156.83	5.553%	$165.5388	$165.54	$165.55	$165.50
Purchase #5	$70.60	13.440%	$80.0886	$80.09	$80.10	$80.10
Purchase #6	$109.49	6.185%	$116.262	$116.26	$116.25	$116.30
Purchase #7	$62.58	4.470%	$65.3773	$65.38	$65.40	$65.40
7 purchase totals =	$720.93		$763.8066	$763.81	$763.85	$763.80