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	$232.70	12.117%	$260.8963	$260.90	$260.90	$260.90
Purchase #2	$86.76	3.623%	$89.9033	$89.90	$89.90	$89.90
Purchase #3	$97.40	7.335%	$104.5443	$104.54	$104.55	$104.50
Purchase #4	$15.96	10.601%	$17.6519	$17.65	$17.65	$17.70
Purchase #5	$211.50	3.832%	$219.6047	$219.60	$219.60	$219.60
Purchase #6	$95.80	4.533%	$100.1426	$100.14	$100.15	$100.10
Purchase #7	$79.75	9.840%	$87.5974	$87.60	$87.60	$87.60
7 purchase totals =	$819.87		$880.3405	$880.33	$880.35	$880.30