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	$33.78	10.504%	$37.3283	$37.33	$37.35	$37.30
Purchase #2	$61.26	8.182%	$66.2723	$66.27	$66.25	$66.30
Purchase #3	$85.45	13.408%	$96.9071	$96.91	$96.90	$96.90
Purchase #4	$139.76	10.462%	$154.3817	$154.38	$154.40	$154.40
Purchase #5	$248.86	12.114%	$279.0069	$279.01	$279.00	$279.00
Purchase #6	$97.32	7.298%	$104.4224	$104.42	$104.40	$104.40
Purchase #7	$90.25	7.446%	$96.97	$96.97	$96.95	$97.00
7 purchase totals =	$756.68		$835.2887	$835.29	$835.25	$835.30