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	$198.72	13.226%	$225.0027	$225.00	$225.00	$225.00
Purchase #2	$141.94	7.810%	$153.0255	$153.03	$153.05	$153.00
Purchase #3	$27.89	13.240%	$31.5826	$31.58	$31.60	$31.60
Purchase #4	$66.39	9.329%	$72.5835	$72.58	$72.60	$72.60
Purchase #5	$44.62	13.848%	$50.799	$50.80	$50.80	$50.80
Purchase #6	$64.85	11.254%	$72.1482	$72.15	$72.15	$72.10
Purchase #7	$103.84	3.292%	$107.2584	$107.26	$107.25	$107.30
7 purchase totals =	$648.25		$712.3999	$712.40	$712.45	$712.40