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	$141.63	10.273%	$156.1796	$156.18	$156.20	$156.20
Purchase #2	$59.31	8.129%	$64.1313	$64.13	$64.15	$64.10
Purchase #3	$152.38	4.325%	$158.9704	$158.97	$158.95	$159.00
Purchase #4	$129.69	10.772%	$143.6602	$143.66	$143.65	$143.70
Purchase #5	$72.96	10.649%	$80.7295	$80.73	$80.75	$80.70
Purchase #6	$205.89	4.854%	$215.8839	$215.88	$215.90	$215.90
Purchase #7	$111.79	10.573%	$123.6096	$123.61	$123.60	$123.60
7 purchase totals =	$873.65		$943.1645	$943.16	$943.20	$943.20