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	$134.40	3.499%	$139.1027	$139.10	$139.10	$139.10
Purchase #2	$100.29	12.553%	$112.8794	$112.88	$112.90	$112.90
Purchase #3	$76.71	3.870%	$79.6787	$79.68	$79.70	$79.70
Purchase #4	$109.90	13.528%	$124.7673	$124.77	$124.75	$124.80
Purchase #5	$100.96	10.266%	$111.3246	$111.32	$111.30	$111.30
Purchase #6	$98.45	4.636%	$103.0141	$103.01	$103.00	$103.00
Purchase #7	$168.82	4.293%	$176.0674	$176.07	$176.05	$176.10
7 purchase totals =	$789.53		$846.8342	$846.83	$846.80	$846.90