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	$23.88	3.180%	$24.6394	$24.64	$24.65	$24.60
Purchase #2	$193.42	3.699%	$200.5746	$200.57	$200.55	$200.60
Purchase #3	$193.81	3.633%	$200.8511	$200.85	$200.85	$200.90
Purchase #4	$49.48	13.749%	$56.283	$56.28	$56.30	$56.30
Purchase #5	$13.45	8.585%	$14.6047	$14.60	$14.60	$14.60
Purchase #6	$22.79	12.286%	$25.59	$25.59	$25.60	$25.60
Purchase #7	$135.81	6.658%	$144.8522	$144.85	$144.85	$144.90
7 purchase totals =	$632.64		$667.3950	$667.38	$667.40	$667.50