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	$113.90	12.186%	$127.7799	$127.78	$127.80	$127.80
Purchase #2	$66.63	9.349%	$72.8592	$72.86	$72.85	$72.90
Purchase #3	$104.25	13.732%	$118.5656	$118.57	$118.55	$118.60
Purchase #4	$163.49	5.472%	$172.4362	$172.44	$172.45	$172.40
Purchase #5	$21.57	5.744%	$22.809	$22.81	$22.80	$22.80
Purchase #6	$112.68	9.286%	$123.1435	$123.14	$123.15	$123.10
Purchase #7	$146.32	4.462%	$152.8488	$152.85	$152.85	$152.80
7 purchase totals =	$728.84		$790.4422	$790.45	$790.45	$790.40