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	$135.65	6.536%	$144.5161	$144.52	$144.50	$144.50
Purchase #2	$157.94	12.222%	$177.2434	$177.24	$177.25	$177.20
Purchase #3	$244.96	5.426%	$258.2515	$258.25	$258.25	$258.30
Purchase #4	$140.32	3.289%	$144.9351	$144.94	$144.95	$144.90
Purchase #5	$239.44	10.832%	$265.3761	$265.38	$265.40	$265.40
Purchase #6	$145.34	6.335%	$154.5473	$154.55	$154.55	$154.50
Purchase #7	$145.59	7.760%	$156.8878	$156.89	$156.90	$156.90
7 purchase totals =	$1,209.24		$1,301.7573	$1,301.77	$1,301.80	$1,301.70