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	$239.69	7.423%	$257.4822	$257.48	$257.50	$257.50
Purchase #2	$52.60	7.147%	$56.3593	$56.36	$56.35	$56.40
Purchase #3	$118.51	4.109%	$123.3796	$123.38	$123.40	$123.40
Purchase #4	$230.40	12.381%	$258.9258	$258.93	$258.95	$258.90
Purchase #5	$56.90	3.211%	$58.7271	$58.73	$58.75	$58.70
Purchase #6	$66.97	7.398%	$71.9244	$71.92	$71.90	$71.90
Purchase #7	$208.54	9.619%	$228.5995	$228.60	$228.60	$228.60
7 purchase totals =	$973.61		$1,055.3979	$1,055.40	$1,055.45	$1,055.40