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	$171.83	11.382%	$191.3877	$191.39	$191.40	$191.40
Purchase #2	$151.31	10.531%	$167.2445	$167.24	$167.25	$167.20
Purchase #3	$174.81	8.606%	$189.8541	$189.85	$189.85	$189.90
Purchase #4	$34.28	13.698%	$38.9757	$38.98	$39.00	$39.00
Purchase #5	$131.52	9.584%	$144.1249	$144.12	$144.10	$144.10
Purchase #6	$25.99	9.404%	$28.4341	$28.43	$28.45	$28.40
Purchase #7	$154.37	5.509%	$162.8742	$162.87	$162.85	$162.90
7 purchase totals =	$844.11		$922.8952	$922.88	$922.90	$922.90