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	$102.56	5.587%	$108.29	$108.29	$108.30	$108.30
Purchase #2	$245.79	8.623%	$266.9845	$266.98	$267.00	$267.00
Purchase #3	$110.99	3.518%	$114.8946	$114.89	$114.90	$114.90
Purchase #4	$41.86	9.255%	$45.7341	$45.73	$45.75	$45.70
Purchase #5	$151.93	13.709%	$172.7581	$172.76	$172.75	$172.80
Purchase #6	$146.59	10.695%	$162.2678	$162.27	$162.25	$162.30
Purchase #7	$29.35	7.647%	$31.5944	$31.59	$31.60	$31.60
7 purchase totals =	$829.07		$902.5235	$902.51	$902.55	$902.60