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	$73.58	5.812%	$77.8565	$77.86	$77.85	$77.90
Purchase #2	$68.52	11.656%	$76.5067	$76.51	$76.50	$76.50
Purchase #3	$87.92	13.208%	$99.5325	$99.53	$99.55	$99.50
Purchase #4	$133.83	8.253%	$144.875	$144.88	$144.90	$144.90
Purchase #5	$103.93	13.412%	$117.8691	$117.87	$117.85	$117.90
Purchase #6	$52.62	13.660%	$59.8079	$59.81	$59.80	$59.80
Purchase #7	$42.68	3.792%	$44.2984	$44.30	$44.30	$44.30
7 purchase totals =	$563.08		$620.7461	$620.76	$620.75	$620.80