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	$21.60	13.122%	$24.4344	$24.43	$24.45	$24.40
Purchase #2	$47.40	11.460%	$52.832	$52.83	$52.85	$52.80
Purchase #3	$97.31	10.215%	$107.2502	$107.25	$107.25	$107.30
Purchase #4	$54.54	10.868%	$60.4674	$60.47	$60.45	$60.50
Purchase #5	$219.83	5.265%	$231.404	$231.40	$231.40	$231.40
Purchase #6	$196.62	11.175%	$218.5923	$218.59	$218.60	$218.60
Purchase #7	$132.31	5.140%	$139.1107	$139.11	$139.10	$139.10
7 purchase totals =	$769.61		$834.0910	$834.08	$834.10	$834.10