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	$62.54	4.604%	$65.4193	$65.42	$65.40	$65.40
Purchase #2	$107.69	9.383%	$117.7946	$117.79	$117.80	$117.80
Purchase #3	$108.66	4.210%	$113.2346	$113.23	$113.25	$113.20
Purchase #4	$246.62	9.257%	$269.4496	$269.45	$269.45	$269.40
Purchase #5	$37.54	5.516%	$39.6107	$39.61	$39.60	$39.60
Purchase #6	$177.61	10.478%	$196.22	$196.22	$196.20	$196.20
Purchase #7	$175.71	9.795%	$192.9208	$192.92	$192.90	$192.90
7 purchase totals =	$916.37		$994.6496	$994.64	$994.60	$994.50