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	$99.82	9.520%	$109.3229	$109.32	$109.30	$109.30
Purchase #2	$138.55	12.466%	$155.8216	$155.82	$155.80	$155.80
Purchase #3	$130.25	10.559%	$144.0031	$144.00	$144.00	$144.00
Purchase #4	$166.78	10.757%	$184.7205	$184.72	$184.70	$184.70
Purchase #5	$129.86	10.393%	$143.3563	$143.36	$143.35	$143.40
Purchase #6	$105.76	11.648%	$118.0789	$118.08	$118.10	$118.10
Purchase #7	$232.57	10.225%	$256.3503	$256.35	$256.35	$256.40
7 purchase totals =	$1,003.59		$1,111.6536	$1,111.65	$1,111.60	$1,111.70