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	$12.64	6.266%	$13.432	$13.43	$13.45	$13.40
Purchase #2	$180.26	3.282%	$186.1761	$186.18	$186.20	$186.20
Purchase #3	$100.43	12.106%	$112.5881	$112.59	$112.60	$112.60
Purchase #4	$79.89	4.542%	$83.5186	$83.52	$83.50	$83.50
Purchase #5	$250.34	5.162%	$263.2626	$263.26	$263.25	$263.30
Purchase #6	$113.81	4.165%	$118.5502	$118.55	$118.55	$118.60
Purchase #7	$247.45	4.798%	$259.3227	$259.32	$259.30	$259.30
7 purchase totals =	$984.82		$1,036.8503	$1,036.85	$1,036.85	$1,036.90