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	$229.94	11.526%	$256.4429	$256.44	$256.45	$256.40
Purchase #2	$144.78	10.827%	$160.4553	$160.46	$160.45	$160.50
Purchase #3	$166.71	7.282%	$178.8498	$178.85	$178.85	$178.80
Purchase #4	$115.94	13.490%	$131.5803	$131.58	$131.60	$131.60
Purchase #5	$126.52	9.579%	$138.6394	$138.64	$138.65	$138.60
Purchase #6	$126.56	13.148%	$143.2001	$143.20	$143.20	$143.20
Purchase #7	$37.62	12.351%	$42.2664	$42.27	$42.25	$42.30
7 purchase totals =	$948.07		$1,051.4342	$1,051.44	$1,051.45	$1,051.40