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	$172.85	8.245%	$187.1015	$187.10	$187.10	$187.10
Purchase #2	$115.35	7.166%	$123.616	$123.62	$123.60	$123.60
Purchase #3	$17.77	9.428%	$19.4454	$19.45	$19.45	$19.40
Purchase #4	$135.63	6.566%	$144.5355	$144.54	$144.55	$144.50
Purchase #5	$146.56	6.459%	$156.0263	$156.03	$156.05	$156.00
Purchase #6	$196.32	12.763%	$221.3763	$221.38	$221.40	$221.40
Purchase #7	$84.83	8.181%	$91.7699	$91.77	$91.75	$91.80
7 purchase totals =	$869.31		$943.8709	$943.89	$943.90	$943.80