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	$107.77	5.432%	$113.6241	$113.62	$113.60	$113.60
Purchase #2	$101.85	12.391%	$114.4702	$114.47	$114.45	$114.50
Purchase #3	$33.67	11.139%	$37.4205	$37.42	$37.40	$37.40
Purchase #4	$183.90	4.505%	$192.1847	$192.18	$192.20	$192.20
Purchase #5	$39.59	5.659%	$41.8304	$41.83	$41.85	$41.80
Purchase #6	$147.82	9.720%	$162.1881	$162.19	$162.20	$162.20
Purchase #7	$219.81	8.174%	$237.7773	$237.78	$237.80	$237.80
7 purchase totals =	$834.41		$899.4953	$899.49	$899.50	$899.50