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	$153.72	12.864%	$173.4945	$173.49	$173.50	$173.50
Purchase #2	$132.35	13.130%	$149.7276	$149.73	$149.75	$149.70
Purchase #3	$180.75	8.734%	$196.5367	$196.54	$196.55	$196.50
Purchase #4	$195.48	12.238%	$219.4028	$219.40	$219.40	$219.40
Purchase #5	$127.55	10.556%	$141.0142	$141.01	$141.00	$141.00
Purchase #6	$113.81	5.837%	$120.4531	$120.45	$120.45	$120.50
Purchase #7	$127.78	6.626%	$136.2467	$136.25	$136.25	$136.20
7 purchase totals =	$1,031.44		$1,136.8756	$1,136.87	$1,136.90	$1,136.80