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	$127.36	9.845%	$139.8986	$139.90	$139.90	$139.90
Purchase #2	$225.25	8.295%	$243.9345	$243.93	$243.95	$243.90
Purchase #3	$165.78	4.304%	$172.9152	$172.92	$172.90	$172.90
Purchase #4	$29.53	10.800%	$32.7192	$32.72	$32.70	$32.70
Purchase #5	$140.49	9.620%	$154.0051	$154.01	$154.00	$154.00
Purchase #6	$186.90	13.114%	$211.4101	$211.41	$211.40	$211.40
Purchase #7	$176.94	8.805%	$192.5196	$192.52	$192.50	$192.50
7 purchase totals =	$1,052.25		$1,147.4023	$1,147.41	$1,147.35	$1,147.30