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	$107.32	10.768%	$118.8762	$118.88	$118.90	$118.90
Purchase #2	$123.78	6.609%	$131.9606	$131.96	$131.95	$132.00
Purchase #3	$152.89	8.870%	$166.4513	$166.45	$166.45	$166.50
Purchase #4	$65.40	3.554%	$67.7243	$67.72	$67.70	$67.70
Purchase #5	$175.45	4.434%	$183.2295	$183.23	$183.25	$183.20
Purchase #6	$114.72	13.725%	$130.4653	$130.47	$130.45	$130.50
Purchase #7	$155.70	8.815%	$169.425	$169.43	$169.45	$169.40
7 purchase totals =	$895.26		$968.1322	$968.14	$968.15	$968.20