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	$10.93	12.182%	$12.2615	$12.26	$12.25	$12.30
Purchase #2	$172.48	9.372%	$188.6448	$188.64	$188.65	$188.60
Purchase #3	$38.49	8.206%	$41.6485	$41.65	$41.65	$41.60
Purchase #4	$46.60	12.130%	$52.2526	$52.25	$52.25	$52.30
Purchase #5	$67.71	3.516%	$70.0907	$70.09	$70.10	$70.10
Purchase #6	$168.38	3.749%	$174.6926	$174.69	$174.70	$174.70
Purchase #7	$85.89	5.687%	$90.7746	$90.77	$90.75	$90.80
7 purchase totals =	$590.48		$630.3653	$630.35	$630.35	$630.40