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	$221.66	5.746%	$234.3966	$234.40	$234.40	$234.40
Purchase #2	$215.51	10.471%	$238.0761	$238.08	$238.10	$238.10
Purchase #3	$191.90	7.564%	$206.4153	$206.42	$206.40	$206.40
Purchase #4	$228.54	6.595%	$243.6122	$243.61	$243.60	$243.60
Purchase #5	$205.45	13.754%	$233.7076	$233.71	$233.70	$233.70
Purchase #6	$82.48	9.108%	$89.9923	$89.99	$90.00	$90.00
Purchase #7	$109.34	6.406%	$116.3443	$116.34	$116.35	$116.30
7 purchase totals =	$1,254.88		$1,362.5444	$1,362.55	$1,362.55	$1,362.50