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	$136.68	12.585%	$153.8812	$153.88	$153.90	$153.90
Purchase #2	$111.39	4.366%	$116.2533	$116.25	$116.25	$116.30
Purchase #3	$101.73	11.585%	$113.5154	$113.52	$113.50	$113.50
Purchase #4	$12.29	8.398%	$13.3221	$13.32	$13.30	$13.30
Purchase #5	$24.73	6.674%	$26.3805	$26.38	$26.40	$26.40
Purchase #6	$72.78	13.349%	$82.4954	$82.50	$82.50	$82.50
Purchase #7	$35.76	8.630%	$38.8461	$38.85	$38.85	$38.80
7 purchase totals =	$495.36		$544.6940	$544.70	$544.70	$544.70