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	$139.73	11.373%	$155.6215	$155.62	$155.60	$155.60
Purchase #2	$45.25	9.136%	$49.384	$49.38	$49.40	$49.40
Purchase #3	$148.73	13.345%	$168.578	$168.58	$168.60	$168.60
Purchase #4	$212.87	5.320%	$224.1947	$224.19	$224.20	$224.20
Purchase #5	$60.35	10.155%	$66.4785	$66.48	$66.50	$66.50
Purchase #6	$58.89	13.642%	$66.9238	$66.92	$66.90	$66.90
Purchase #7	$46.79	5.677%	$49.4463	$49.45	$49.45	$49.40
7 purchase totals =	$712.61		$780.6268	$780.62	$780.65	$780.60