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	$83.89	7.838%	$90.4653	$90.47	$90.45	$90.50
Purchase #2	$177.89	8.355%	$192.7527	$192.75	$192.75	$192.80
Purchase #3	$12.27	6.689%	$13.0907	$13.09	$13.10	$13.10
Purchase #4	$191.64	3.585%	$198.5103	$198.51	$198.50	$198.50
Purchase #5	$107.51	5.588%	$113.5177	$113.52	$113.50	$113.50
Purchase #6	$25.81	8.215%	$27.9303	$27.93	$27.95	$27.90
Purchase #7	$13.92	3.575%	$14.4176	$14.42	$14.40	$14.40
7 purchase totals =	$612.93		$650.6846	$650.69	$650.65	$650.70