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	$144.35	4.516%	$150.8688	$150.87	$150.85	$150.90
Purchase #2	$91.50	10.158%	$100.7946	$100.79	$100.80	$100.80
Purchase #3	$166.55	10.377%	$183.8329	$183.83	$183.85	$183.80
Purchase #4	$128.42	9.113%	$140.1229	$140.12	$140.10	$140.10
Purchase #5	$127.79	8.305%	$138.403	$138.40	$138.40	$138.40
Purchase #6	$38.79	9.103%	$42.3211	$42.32	$42.30	$42.30
Purchase #7	$81.61	13.389%	$92.5368	$92.54	$92.55	$92.50
7 purchase totals =	$779.01		$848.8801	$848.87	$848.85	$848.80