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	$241.54	9.423%	$264.3003	$264.30	$264.30	$264.30
Purchase #2	$227.83	5.124%	$239.504	$239.50	$239.50	$239.50
Purchase #3	$47.72	10.336%	$52.6523	$52.65	$52.65	$52.70
Purchase #4	$65.29	13.756%	$74.2713	$74.27	$74.25	$74.30
Purchase #5	$43.96	10.372%	$48.5195	$48.52	$48.50	$48.50
Purchase #6	$113.75	8.660%	$123.6008	$123.60	$123.60	$123.60
Purchase #7	$186.37	7.639%	$200.6068	$200.61	$200.60	$200.60
7 purchase totals =	$926.46		$1,003.4550	$1,003.45	$1,003.40	$1,003.50