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	$208.31	7.726%	$224.404	$224.40	$224.40	$224.40
Purchase #2	$176.34	11.604%	$196.8025	$196.80	$196.80	$196.80
Purchase #3	$73.78	10.158%	$81.2746	$81.27	$81.25	$81.30
Purchase #4	$104.60	6.470%	$111.3676	$111.37	$111.35	$111.40
Purchase #5	$132.92	6.544%	$141.6183	$141.62	$141.60	$141.60
Purchase #6	$155.37	11.830%	$173.7503	$173.75	$173.75	$173.80
Purchase #7	$36.41	7.839%	$39.2642	$39.26	$39.25	$39.30
7 purchase totals =	$887.73		$968.4815	$968.47	$968.40	$968.60