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	$28.69	9.611%	$31.4474	$31.45	$31.45	$31.40
Purchase #2	$148.78	5.552%	$157.0403	$157.04	$157.05	$157.00
Purchase #3	$26.78	5.502%	$28.2534	$28.25	$28.25	$28.30
Purchase #4	$65.75	5.516%	$69.3768	$69.38	$69.40	$69.40
Purchase #5	$107.76	5.238%	$113.4045	$113.40	$113.40	$113.40
Purchase #6	$76.55	9.193%	$83.5872	$83.59	$83.60	$83.60
Purchase #7	$148.34	5.486%	$156.4779	$156.48	$156.50	$156.50
7 purchase totals =	$602.65		$639.5875	$639.59	$639.65	$639.60