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	$31.28	11.257%	$34.8012	$34.80	$34.80	$34.80
Purchase #2	$89.38	11.304%	$99.4835	$99.48	$99.50	$99.50
Purchase #3	$29.26	8.795%	$31.8334	$31.83	$31.85	$31.80
Purchase #4	$141.87	12.380%	$159.4335	$159.43	$159.45	$159.40
Purchase #5	$105.72	7.450%	$113.5961	$113.60	$113.60	$113.60
Purchase #6	$135.38	12.830%	$152.7493	$152.75	$152.75	$152.70
Purchase #7	$40.36	10.470%	$44.5857	$44.59	$44.60	$44.60
7 purchase totals =	$573.25		$636.4827	$636.48	$636.55	$636.40