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	$126.52	9.761%	$138.8696	$138.87	$138.85	$138.90
Purchase #2	$106.52	10.399%	$117.597	$117.60	$117.60	$117.60
Purchase #3	$89.51	11.534%	$99.8341	$99.83	$99.85	$99.80
Purchase #4	$166.62	10.399%	$183.9468	$183.95	$183.95	$183.90
Purchase #5	$95.25	11.201%	$105.919	$105.92	$105.90	$105.90
Purchase #6	$49.49	12.834%	$55.8415	$55.84	$55.85	$55.80
Purchase #7	$224.50	10.285%	$247.5898	$247.59	$247.60	$247.60
7 purchase totals =	$858.41		$949.5978	$949.60	$949.60	$949.50