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	$135.67	6.652%	$144.6948	$144.69	$144.70	$144.70
Purchase #2	$216.42	4.102%	$225.2975	$225.30	$225.30	$225.30
Purchase #3	$111.96	10.448%	$123.6576	$123.66	$123.65	$123.70
Purchase #4	$224.96	10.399%	$248.3536	$248.35	$248.35	$248.40
Purchase #5	$184.87	3.260%	$190.8968	$190.90	$190.90	$190.90
Purchase #6	$74.94	4.366%	$78.2119	$78.21	$78.20	$78.20
Purchase #7	$192.34	8.601%	$208.8832	$208.88	$208.90	$208.90
7 purchase totals =	$1,141.16		$1,219.9954	$1,219.99	$1,220.00	$1,220.10