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	$129.39	6.116%	$137.3035	$137.30	$137.30	$137.30
Purchase #2	$118.75	9.234%	$129.7154	$129.72	$129.70	$129.70
Purchase #3	$54.91	3.638%	$56.9076	$56.91	$56.90	$56.90
Purchase #4	$85.73	6.825%	$91.5811	$91.58	$91.60	$91.60
Purchase #5	$139.46	6.603%	$148.6685	$148.67	$148.65	$148.70
Purchase #6	$246.73	13.286%	$279.5105	$279.51	$279.50	$279.50
Purchase #7	$104.94	4.105%	$109.2478	$109.25	$109.25	$109.20
7 purchase totals =	$879.91		$952.9344	$952.94	$952.90	$952.90