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	$80.81	3.730%	$83.8242	$83.82	$83.80	$83.80
Purchase #2	$99.94	4.324%	$104.2614	$104.26	$104.25	$104.30
Purchase #3	$123.90	12.595%	$139.5052	$139.51	$139.50	$139.50
Purchase #4	$156.42	6.498%	$166.5842	$166.58	$166.60	$166.60
Purchase #5	$237.35	8.375%	$257.2281	$257.23	$257.25	$257.20
Purchase #6	$63.96	11.215%	$71.1331	$71.13	$71.15	$71.10
Purchase #7	$97.25	3.298%	$100.4573	$100.46	$100.45	$100.50
7 purchase totals =	$859.63		$922.9935	$922.99	$923.00	$923.00