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	$15.49	13.587%	$17.5946	$17.59	$17.60	$17.60
Purchase #2	$249.30	12.136%	$279.555	$279.56	$279.55	$279.60
Purchase #3	$221.30	4.116%	$230.4087	$230.41	$230.40	$230.40
Purchase #4	$242.77	13.688%	$276.0004	$276.00	$276.00	$276.00
Purchase #5	$39.81	7.850%	$42.9351	$42.94	$42.95	$42.90
Purchase #6	$63.69	4.282%	$66.4172	$66.42	$66.40	$66.40
Purchase #7	$199.97	9.289%	$218.5452	$218.55	$218.55	$218.50
7 purchase totals =	$1,032.33		$1,131.4562	$1,131.47	$1,131.45	$1,131.40