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	$28.42	10.692%	$31.4587	$31.46	$31.45	$31.50
Purchase #2	$160.55	3.632%	$166.3812	$166.38	$166.40	$166.40
Purchase #3	$92.85	6.371%	$98.7655	$98.77	$98.75	$98.80
Purchase #4	$139.72	3.665%	$144.8407	$144.84	$144.85	$144.80
Purchase #5	$109.94	7.684%	$118.3878	$118.39	$118.40	$118.40
Purchase #6	$217.56	6.785%	$232.3214	$232.32	$232.30	$232.30
Purchase #7	$87.94	4.288%	$91.7109	$91.71	$91.70	$91.70
7 purchase totals =	$836.98		$883.8662	$883.87	$883.85	$883.90