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	$37.40	5.593%	$39.4918	$39.49	$39.50	$39.50
Purchase #2	$32.34	3.456%	$33.4577	$33.46	$33.45	$33.50
Purchase #3	$79.69	11.250%	$88.6551	$88.66	$88.65	$88.70
Purchase #4	$44.49	8.650%	$48.3384	$48.34	$48.35	$48.30
Purchase #5	$59.46	12.244%	$66.7403	$66.74	$66.75	$66.70
Purchase #6	$238.34	4.775%	$249.7207	$249.72	$249.70	$249.70
Purchase #7	$139.91	11.627%	$156.1773	$156.18	$156.20	$156.20
7 purchase totals =	$631.63		$682.5813	$682.59	$682.60	$682.60