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	$58.88	13.420%	$66.7817	$66.78	$66.80	$66.80
Purchase #2	$106.44	11.176%	$118.3357	$118.34	$118.35	$118.30
Purchase #3	$132.75	9.684%	$145.6055	$145.61	$145.60	$145.60
Purchase #4	$48.58	8.284%	$52.6044	$52.60	$52.60	$52.60
Purchase #5	$73.59	12.226%	$82.5871	$82.59	$82.60	$82.60
Purchase #6	$165.66	10.468%	$183.0013	$183.00	$183.00	$183.00
Purchase #7	$135.54	12.780%	$152.862	$152.86	$152.85	$152.90
7 purchase totals =	$721.44		$801.7777	$801.78	$801.80	$801.80