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	$76.43	5.383%	$80.5442	$80.54	$80.55	$80.50
Purchase #2	$134.40	11.721%	$150.153	$150.15	$150.15	$150.20
Purchase #3	$222.49	10.527%	$245.9115	$245.91	$245.90	$245.90
Purchase #4	$216.48	11.128%	$240.5699	$240.57	$240.55	$240.60
Purchase #5	$39.76	3.120%	$41.0005	$41.00	$41.00	$41.00
Purchase #6	$9.50	9.403%	$10.3933	$10.39	$10.40	$10.40
Purchase #7	$80.65	12.665%	$90.8643	$90.86	$90.85	$90.90
7 purchase totals =	$779.71		$859.4367	$859.42	$859.40	$859.50