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	$10.27	11.270%	$11.4274	$11.43	$11.45	$11.40
Purchase #2	$127.58	10.337%	$140.7679	$140.77	$140.75	$140.80
Purchase #3	$33.82	10.863%	$37.4939	$37.49	$37.50	$37.50
Purchase #4	$145.75	9.413%	$159.4694	$159.47	$159.45	$159.50
Purchase #5	$41.97	3.196%	$43.3114	$43.31	$43.30	$43.30
Purchase #6	$56.60	9.408%	$61.9249	$61.92	$61.90	$61.90
Purchase #7	$57.72	3.712%	$59.8626	$59.86	$59.85	$59.90
7 purchase totals =	$473.71		$514.2575	$514.25	$514.20	$514.30