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	$22.81	3.124%	$23.5226	$23.52	$23.50	$23.50
Purchase #2	$187.74	4.854%	$196.8529	$196.85	$196.85	$196.90
Purchase #3	$21.39	5.766%	$22.6233	$22.62	$22.60	$22.60
Purchase #4	$40.47	8.511%	$43.9144	$43.91	$43.90	$43.90
Purchase #5	$183.72	9.342%	$200.8831	$200.88	$200.90	$200.90
Purchase #6	$165.37	13.672%	$187.9794	$187.98	$188.00	$188.00
Purchase #7	$177.72	11.349%	$197.8894	$197.89	$197.90	$197.90
7 purchase totals =	$799.22		$873.6651	$873.65	$873.65	$873.70