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	$29.76	8.587%	$32.3155	$32.32	$32.30	$32.30
Purchase #2	$36.69	7.614%	$39.4836	$39.48	$39.50	$39.50
Purchase #3	$143.61	7.455%	$154.3161	$154.32	$154.30	$154.30
Purchase #4	$16.71	10.420%	$18.4512	$18.45	$18.45	$18.50
Purchase #5	$81.86	13.461%	$92.8792	$92.88	$92.90	$92.90
Purchase #6	$104.75	5.147%	$110.1415	$110.14	$110.15	$110.10
Purchase #7	$105.85	12.699%	$119.2919	$119.29	$119.30	$119.30
7 purchase totals =	$519.23		$566.8790	$566.88	$566.90	$566.90