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	$112.83	9.339%	$123.3672	$123.37	$123.35	$123.40
Purchase #2	$196.91	11.522%	$219.598	$219.60	$219.60	$219.60
Purchase #3	$119.52	3.116%	$123.2442	$123.24	$123.25	$123.20
Purchase #4	$156.81	12.598%	$176.5649	$176.56	$176.55	$176.60
Purchase #5	$63.76	13.802%	$72.5602	$72.56	$72.55	$72.60
Purchase #6	$215.81	10.736%	$238.9794	$238.98	$239.00	$239.00
Purchase #7	$107.65	4.329%	$112.3102	$112.31	$112.30	$112.30
7 purchase totals =	$973.29		$1,066.6241	$1,066.62	$1,066.60	$1,066.70