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	$234.45	12.572%	$263.9251	$263.93	$263.95	$263.90
Purchase #2	$136.93	12.375%	$153.8751	$153.88	$153.90	$153.90
Purchase #3	$40.49	8.748%	$44.0321	$44.03	$44.05	$44.00
Purchase #4	$25.94	13.866%	$29.5368	$29.54	$29.55	$29.50
Purchase #5	$129.28	12.759%	$145.7748	$145.77	$145.75	$145.80
Purchase #6	$54.44	9.439%	$59.5786	$59.58	$59.60	$59.60
Purchase #7	$196.57	10.202%	$216.6241	$216.62	$216.60	$216.60
7 purchase totals =	$818.10		$913.3466	$913.35	$913.40	$913.30