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	$249.49	8.171%	$269.8758	$269.88	$269.90	$269.90
Purchase #2	$101.44	6.127%	$107.6552	$107.66	$107.65	$107.70
Purchase #3	$216.31	11.532%	$241.2549	$241.25	$241.25	$241.30
Purchase #4	$86.92	10.169%	$95.7589	$95.76	$95.75	$95.80
Purchase #5	$34.64	6.535%	$36.9037	$36.90	$36.90	$36.90
Purchase #6	$80.76	11.214%	$89.8164	$89.82	$89.80	$89.80
Purchase #7	$128.29	12.697%	$144.579	$144.58	$144.60	$144.60
7 purchase totals =	$897.85		$985.8439	$985.85	$985.85	$986.00