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	$80.50	10.594%	$89.0282	$89.03	$89.05	$89.00
Purchase #2	$213.78	13.707%	$243.0828	$243.08	$243.10	$243.10
Purchase #3	$81.33	6.377%	$86.5164	$86.52	$86.50	$86.50
Purchase #4	$236.87	6.342%	$251.8923	$251.89	$251.90	$251.90
Purchase #5	$54.60	3.573%	$56.5509	$56.55	$56.55	$56.60
Purchase #6	$119.47	3.149%	$123.2321	$123.23	$123.25	$123.20
Purchase #7	$46.94	11.477%	$52.3273	$52.33	$52.35	$52.30
7 purchase totals =	$833.49		$902.6300	$902.63	$902.70	$902.60