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	$205.47	3.420%	$212.4971	$212.50	$212.50	$212.50
Purchase #2	$190.99	9.570%	$209.2677	$209.27	$209.25	$209.30
Purchase #3	$178.30	10.530%	$197.075	$197.08	$197.10	$197.10
Purchase #4	$118.61	11.698%	$132.485	$132.49	$132.50	$132.50
Purchase #5	$107.72	3.134%	$111.0959	$111.10	$111.10	$111.10
Purchase #6	$21.79	3.668%	$22.5893	$22.59	$22.60	$22.60
Purchase #7	$67.56	6.358%	$71.8555	$71.86	$71.85	$71.90
7 purchase totals =	$890.44		$956.8655	$956.89	$956.90	$957.00