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	$108.93	4.209%	$113.5149	$113.51	$113.50	$113.50
Purchase #2	$225.35	7.691%	$242.6817	$242.68	$242.70	$242.70
Purchase #3	$145.59	3.263%	$150.3406	$150.34	$150.35	$150.30
Purchase #4	$130.91	11.559%	$146.0419	$146.04	$146.05	$146.00
Purchase #5	$141.62	8.519%	$153.6846	$153.68	$153.70	$153.70
Purchase #6	$90.56	11.344%	$100.8331	$100.83	$100.85	$100.80
Purchase #7	$186.54	10.186%	$205.541	$205.54	$205.55	$205.50
7 purchase totals =	$1,029.50		$1,112.6378	$1,112.62	$1,112.70	$1,112.50