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	$160.51	10.225%	$176.9221	$176.92	$176.90	$176.90
Purchase #2	$176.95	9.443%	$193.6594	$193.66	$193.65	$193.70
Purchase #3	$30.83	13.335%	$34.9412	$34.94	$34.95	$34.90
Purchase #4	$53.82	3.688%	$55.8049	$55.80	$55.80	$55.80
Purchase #5	$57.34	13.833%	$65.2718	$65.27	$65.25	$65.30
Purchase #6	$68.74	5.739%	$72.685	$72.69	$72.70	$72.70
Purchase #7	$39.71	7.204%	$42.5707	$42.57	$42.55	$42.60
7 purchase totals =	$587.90		$641.8551	$641.85	$641.80	$641.90