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	$181.55	8.174%	$196.3899	$196.39	$196.40	$196.40
Purchase #2	$132.40	11.831%	$148.0642	$148.06	$148.05	$148.10
Purchase #3	$133.49	5.838%	$141.2831	$141.28	$141.30	$141.30
Purchase #4	$106.37	8.685%	$115.6082	$115.61	$115.60	$115.60
Purchase #5	$22.77	5.530%	$24.0292	$24.03	$24.05	$24.00
Purchase #6	$59.47	5.345%	$62.6487	$62.65	$62.65	$62.60
Purchase #7	$215.73	12.553%	$242.8106	$242.81	$242.80	$242.80
7 purchase totals =	$851.78		$930.8339	$930.83	$930.85	$930.80