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	$51.36	4.168%	$53.5007	$53.50	$53.50	$53.50
Purchase #2	$23.93	9.755%	$26.2644	$26.26	$26.25	$26.30
Purchase #3	$128.50	9.598%	$140.8334	$140.83	$140.85	$140.80
Purchase #4	$89.69	4.102%	$93.3691	$93.37	$93.35	$93.40
Purchase #5	$10.28	5.602%	$10.8559	$10.86	$10.85	$10.90
Purchase #6	$144.86	6.159%	$153.7819	$153.78	$153.80	$153.80
Purchase #7	$54.52	3.841%	$56.6141	$56.61	$56.60	$56.60
7 purchase totals =	$503.14		$535.2195	$535.21	$535.20	$535.30