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	$38.35	9.668%	$42.0577	$42.06	$42.05	$42.10
Purchase #2	$122.47	11.366%	$136.3899	$136.39	$136.40	$136.40
Purchase #3	$177.37	6.852%	$189.5234	$189.52	$189.50	$189.50
Purchase #4	$188.66	10.779%	$208.9957	$209.00	$209.00	$209.00
Purchase #5	$50.43	9.661%	$55.302	$55.30	$55.30	$55.30
Purchase #6	$202.95	13.698%	$230.7501	$230.75	$230.75	$230.80
Purchase #7	$148.48	3.593%	$153.8149	$153.81	$153.80	$153.80
7 purchase totals =	$928.71		$1,016.8337	$1,016.83	$1,016.80	$1,016.90