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	$139.97	3.189%	$144.4336	$144.43	$144.45	$144.40
Purchase #2	$114.61	13.782%	$130.4056	$130.41	$130.40	$130.40
Purchase #3	$169.59	7.844%	$182.8926	$182.89	$182.90	$182.90
Purchase #4	$158.88	8.479%	$172.3514	$172.35	$172.35	$172.40
Purchase #5	$49.36	11.583%	$55.0774	$55.08	$55.10	$55.10
Purchase #6	$61.51	8.350%	$66.6461	$66.65	$66.65	$66.60
Purchase #7	$105.58	3.864%	$109.6596	$109.66	$109.65	$109.70
7 purchase totals =	$799.50		$861.4663	$861.47	$861.50	$861.50