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	$247.78	12.864%	$279.6544	$279.65	$279.65	$279.70
Purchase #2	$69.94	12.813%	$78.9014	$78.90	$78.90	$78.90
Purchase #3	$205.78	13.472%	$233.5027	$233.50	$233.50	$233.50
Purchase #4	$216.42	4.825%	$226.8623	$226.86	$226.85	$226.90
Purchase #5	$176.47	12.787%	$199.0352	$199.04	$199.05	$199.00
Purchase #6	$235.39	9.778%	$258.4064	$258.41	$258.40	$258.40
Purchase #7	$157.26	7.211%	$168.6	$168.60	$168.60	$168.60
7 purchase totals =	$1,309.04		$1,444.9624	$1,444.96	$1,444.95	$1,445.00