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	$109.30	10.142%	$120.3852	$120.39	$120.40	$120.40
Purchase #2	$5.32	12.212%	$5.9697	$5.97	$5.95	$6.00
Purchase #3	$62.25	6.585%	$66.3492	$66.35	$66.35	$66.30
Purchase #4	$196.41	9.593%	$215.2516	$215.25	$215.25	$215.30
Purchase #5	$43.96	11.243%	$48.9024	$48.90	$48.90	$48.90
Purchase #6	$238.43	5.629%	$251.8512	$251.85	$251.85	$251.90
Purchase #7	$76.89	11.358%	$85.6232	$85.62	$85.60	$85.60
7 purchase totals =	$732.56		$794.3325	$794.33	$794.30	$794.40