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	$234.83	7.141%	$251.5992	$251.60	$251.60	$251.60
Purchase #2	$37.89	13.768%	$43.1067	$43.11	$43.10	$43.10
Purchase #3	$38.85	3.286%	$40.1266	$40.13	$40.15	$40.10
Purchase #4	$104.40	12.681%	$117.639	$117.64	$117.65	$117.60
Purchase #5	$124.72	8.148%	$134.8822	$134.88	$134.90	$134.90
Purchase #6	$39.50	10.204%	$43.5306	$43.53	$43.55	$43.50
Purchase #7	$206.60	7.703%	$222.5144	$222.51	$222.50	$222.50
7 purchase totals =	$786.79		$853.3987	$853.40	$853.45	$853.30