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	$145.59	12.405%	$163.6504	$163.65	$163.65	$163.70
Purchase #2	$33.39	13.446%	$37.8796	$37.88	$37.90	$37.90
Purchase #3	$114.27	3.400%	$118.1552	$118.16	$118.15	$118.20
Purchase #4	$21.85	12.332%	$24.5445	$24.54	$24.55	$24.50
Purchase #5	$9.95	6.328%	$10.5796	$10.58	$10.60	$10.60
Purchase #6	$87.55	3.736%	$90.8209	$90.82	$90.80	$90.80
Purchase #7	$54.29	6.407%	$57.7684	$57.77	$57.75	$57.80
7 purchase totals =	$466.89		$503.3986	$503.40	$503.40	$503.50