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	$37.65	8.519%	$40.8574	$40.86	$40.85	$40.90
Purchase #2	$123.81	8.651%	$134.5208	$134.52	$134.50	$134.50
Purchase #3	$87.87	9.855%	$96.5296	$96.53	$96.55	$96.50
Purchase #4	$62.95	11.841%	$70.4039	$70.40	$70.40	$70.40
Purchase #5	$73.70	13.783%	$83.8581	$83.86	$83.85	$83.90
Purchase #6	$167.95	10.294%	$185.2388	$185.24	$185.25	$185.20
Purchase #7	$62.59	5.681%	$66.1457	$66.15	$66.15	$66.10
7 purchase totals =	$616.52		$677.5543	$677.56	$677.55	$677.50