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	$72.78	10.592%	$80.4889	$80.49	$80.50	$80.50
Purchase #2	$133.66	5.356%	$140.8188	$140.82	$140.80	$140.80
Purchase #3	$249.26	10.451%	$275.3102	$275.31	$275.30	$275.30
Purchase #4	$153.36	13.245%	$173.6725	$173.67	$173.65	$173.70
Purchase #5	$225.75	13.221%	$255.5964	$255.60	$255.60	$255.60
Purchase #6	$232.87	10.582%	$257.5123	$257.51	$257.50	$257.50
Purchase #7	$53.66	3.254%	$55.4061	$55.41	$55.40	$55.40
7 purchase totals =	$1,121.34		$1,238.8052	$1,238.81	$1,238.75	$1,238.80