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	$92.58	10.247%	$102.0667	$102.07	$102.05	$102.10
Purchase #2	$200.83	10.715%	$222.3489	$222.35	$222.35	$222.30
Purchase #3	$226.89	8.153%	$245.3883	$245.39	$245.40	$245.40
Purchase #4	$192.85	11.784%	$215.5754	$215.58	$215.60	$215.60
Purchase #5	$150.85	10.159%	$166.1749	$166.17	$166.15	$166.20
Purchase #6	$250.55	6.341%	$266.4374	$266.44	$266.45	$266.40
Purchase #7	$81.56	13.271%	$92.3838	$92.38	$92.40	$92.40
7 purchase totals =	$1,196.11		$1,310.3754	$1,310.38	$1,310.40	$1,310.40