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	$100.39	3.311%	$103.7139	$103.71	$103.70	$103.70
Purchase #2	$134.86	6.761%	$143.9779	$143.98	$144.00	$144.00
Purchase #3	$211.59	13.143%	$239.3993	$239.40	$239.40	$239.40
Purchase #4	$53.72	7.647%	$57.828	$57.83	$57.85	$57.80
Purchase #5	$209.91	4.127%	$218.573	$218.57	$218.55	$218.60
Purchase #6	$207.89	12.738%	$234.371	$234.37	$234.35	$234.40
Purchase #7	$244.51	13.397%	$277.267	$277.27	$277.25	$277.30
7 purchase totals =	$1,162.87		$1,275.1301	$1,275.13	$1,275.10	$1,275.20