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	$249.38	9.402%	$272.8267	$272.83	$272.85	$272.80
Purchase #2	$159.46	8.855%	$173.5802	$173.58	$173.60	$173.60
Purchase #3	$181.90	4.307%	$189.7344	$189.73	$189.75	$189.70
Purchase #4	$141.27	10.375%	$155.9268	$155.93	$155.95	$155.90
Purchase #5	$81.61	11.312%	$90.8417	$90.84	$90.85	$90.80
Purchase #6	$40.36	5.578%	$42.6113	$42.61	$42.60	$42.60
Purchase #7	$227.83	11.139%	$253.208	$253.21	$253.20	$253.20
7 purchase totals =	$1,081.81		$1,178.7291	$1,178.73	$1,178.80	$1,178.60