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	$50.60	9.613%	$55.4642	$55.46	$55.45	$55.50
Purchase #2	$246.42	10.781%	$272.9865	$272.99	$273.00	$273.00
Purchase #3	$234.50	10.128%	$258.2502	$258.25	$258.25	$258.30
Purchase #4	$100.90	6.358%	$107.3152	$107.32	$107.30	$107.30
Purchase #5	$183.42	8.555%	$199.1116	$199.11	$199.10	$199.10
Purchase #6	$180.35	9.156%	$196.8628	$196.86	$196.85	$196.90
Purchase #7	$239.70	12.405%	$269.4348	$269.43	$269.45	$269.40
7 purchase totals =	$1,235.89		$1,359.4253	$1,359.42	$1,359.40	$1,359.50