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	$45.32	5.458%	$47.7936	$47.79	$47.80	$47.80
Purchase #2	$133.57	3.193%	$137.8349	$137.83	$137.85	$137.80
Purchase #3	$105.60	13.146%	$119.4822	$119.48	$119.50	$119.50
Purchase #4	$97.73	13.768%	$111.1855	$111.19	$111.20	$111.20
Purchase #5	$36.66	5.427%	$38.6495	$38.65	$38.65	$38.60
Purchase #6	$131.94	5.472%	$139.1598	$139.16	$139.15	$139.20
Purchase #7	$76.74	6.227%	$81.5186	$81.52	$81.50	$81.50
7 purchase totals =	$627.56		$675.6241	$675.62	$675.65	$675.60