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	$87.33	3.112%	$90.0477	$90.05	$90.05	$90.00
Purchase #2	$226.82	10.215%	$249.9897	$249.99	$250.00	$250.00
Purchase #3	$221.60	12.587%	$249.4928	$249.49	$249.50	$249.50
Purchase #4	$86.26	9.548%	$94.4961	$94.50	$94.50	$94.50
Purchase #5	$62.35	12.734%	$70.2896	$70.29	$70.30	$70.30
Purchase #6	$183.52	6.185%	$194.8707	$194.87	$194.85	$194.90
Purchase #7	$131.91	9.407%	$144.3188	$144.32	$144.30	$144.30
7 purchase totals =	$999.79		$1,093.5054	$1,093.51	$1,093.50	$1,093.50