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	$106.35	5.500%	$112.1993	$112.20	$112.20	$112.20
Purchase #2	$143.59	10.273%	$158.341	$158.34	$158.35	$158.30
Purchase #3	$190.70	10.784%	$211.2651	$211.27	$211.25	$211.30
Purchase #4	$76.76	13.294%	$86.9645	$86.96	$86.95	$87.00
Purchase #5	$135.49	11.414%	$150.9548	$150.95	$150.95	$151.00
Purchase #6	$95.38	5.464%	$100.5916	$100.59	$100.60	$100.60
Purchase #7	$153.88	9.572%	$168.6094	$168.61	$168.60	$168.60
7 purchase totals =	$902.15		$988.9257	$988.92	$988.90	$989.00