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	$103.30	13.710%	$117.4624	$117.46	$117.45	$117.50
Purchase #2	$75.47	4.237%	$78.6677	$78.67	$78.65	$78.70
Purchase #3	$44.54	7.391%	$47.832	$47.83	$47.85	$47.80
Purchase #4	$232.30	10.401%	$256.4615	$256.46	$256.45	$256.50
Purchase #5	$118.27	7.727%	$127.4087	$127.41	$127.40	$127.40
Purchase #6	$178.70	12.133%	$200.3817	$200.38	$200.40	$200.40
Purchase #7	$38.94	8.265%	$42.1584	$42.16	$42.15	$42.20
7 purchase totals =	$791.52		$870.3724	$870.37	$870.35	$870.50