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	$38.88	7.716%	$41.88	$41.88	$41.90	$41.90
Purchase #2	$226.61	10.139%	$249.586	$249.59	$249.60	$249.60
Purchase #3	$244.97	6.322%	$260.457	$260.46	$260.45	$260.50
Purchase #4	$164.51	13.339%	$186.454	$186.45	$186.45	$186.50
Purchase #5	$54.42	3.397%	$56.2686	$56.27	$56.25	$56.30
Purchase #6	$18.69	9.289%	$20.4261	$20.43	$20.45	$20.40
Purchase #7	$82.85	4.860%	$86.8765	$86.88	$86.90	$86.90
7 purchase totals =	$830.93		$901.9482	$901.96	$902.00	$902.10