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	$102.58	10.454%	$113.3037	$113.30	$113.30	$113.30
Purchase #2	$38.31	12.801%	$43.2141	$43.21	$43.20	$43.20
Purchase #3	$171.95	13.562%	$195.2699	$195.27	$195.25	$195.30
Purchase #4	$30.57	7.854%	$32.971	$32.97	$32.95	$33.00
Purchase #5	$50.40	4.563%	$52.6998	$52.70	$52.70	$52.70
Purchase #6	$107.79	3.318%	$111.3665	$111.37	$111.35	$111.40
Purchase #7	$117.99	11.530%	$131.5942	$131.59	$131.60	$131.60
7 purchase totals =	$619.59		$680.4192	$680.41	$680.35	$680.50