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	$24.51	13.632%	$27.8512	$27.85	$27.85	$27.90
Purchase #2	$171.95	5.554%	$181.5001	$181.50	$181.50	$181.50
Purchase #3	$46.66	13.461%	$52.9409	$52.94	$52.95	$52.90
Purchase #4	$232.54	6.422%	$247.4737	$247.47	$247.45	$247.50
Purchase #5	$42.57	13.661%	$48.3855	$48.39	$48.40	$48.40
Purchase #6	$83.82	11.178%	$93.1894	$93.19	$93.20	$93.20
Purchase #7	$233.70	9.761%	$256.5115	$256.51	$256.50	$256.50
7 purchase totals =	$835.75		$907.8523	$907.85	$907.85	$907.90