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	$95.92	12.737%	$108.1373	$108.14	$108.15	$108.10
Purchase #2	$77.65	10.646%	$85.9166	$85.92	$85.90	$85.90
Purchase #3	$139.25	13.560%	$158.1323	$158.13	$158.15	$158.10
Purchase #4	$199.25	12.471%	$224.0985	$224.10	$224.10	$224.10
Purchase #5	$148.51	9.308%	$162.3333	$162.33	$162.35	$162.30
Purchase #6	$105.90	6.462%	$112.7433	$112.74	$112.75	$112.70
Purchase #7	$132.54	8.109%	$143.2877	$143.29	$143.30	$143.30
7 purchase totals =	$899.02		$994.6490	$994.65	$994.70	$994.50