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	$230.51	12.312%	$258.8904	$258.89	$258.90	$258.90
Purchase #2	$237.96	8.627%	$258.4888	$258.49	$258.50	$258.50
Purchase #3	$144.91	13.406%	$164.3366	$164.34	$164.35	$164.30
Purchase #4	$137.80	9.337%	$150.6664	$150.67	$150.65	$150.70
Purchase #5	$209.55	3.487%	$216.857	$216.86	$216.85	$216.90
Purchase #6	$87.97	8.641%	$95.5715	$95.57	$95.55	$95.60
Purchase #7	$116.40	5.688%	$123.0208	$123.02	$123.00	$123.00
7 purchase totals =	$1,165.10		$1,267.8315	$1,267.84	$1,267.80	$1,267.90