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	$58.73	11.849%	$65.6889	$65.69	$65.70	$65.70
Purchase #2	$121.86	7.873%	$131.454	$131.45	$131.45	$131.50
Purchase #3	$181.53	10.136%	$199.9299	$199.93	$199.95	$199.90
Purchase #4	$126.49	8.246%	$136.9204	$136.92	$136.90	$136.90
Purchase #5	$12.32	12.608%	$13.8733	$13.87	$13.85	$13.90
Purchase #6	$45.59	12.610%	$51.3389	$51.34	$51.35	$51.30
Purchase #7	$61.78	5.595%	$65.2366	$65.24	$65.25	$65.20
7 purchase totals =	$608.30		$664.4420	$664.44	$664.45	$664.40