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	$119.53	12.177%	$134.0852	$134.09	$134.10	$134.10
Purchase #2	$194.41	5.540%	$205.1803	$205.18	$205.20	$205.20
Purchase #3	$111.87	11.659%	$124.9129	$124.91	$124.90	$124.90
Purchase #4	$63.73	13.829%	$72.5432	$72.54	$72.55	$72.50
Purchase #5	$70.97	10.189%	$78.2011	$78.20	$78.20	$78.20
Purchase #6	$51.73	9.823%	$56.8114	$56.81	$56.80	$56.80
Purchase #7	$229.43	12.521%	$258.1569	$258.16	$258.15	$258.20
7 purchase totals =	$841.67		$929.8910	$929.89	$929.90	$929.90