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	$201.39	9.732%	$220.9893	$220.99	$221.00	$221.00
Purchase #2	$59.66	13.146%	$67.5029	$67.50	$67.50	$67.50
Purchase #3	$113.57	12.333%	$127.5766	$127.58	$127.60	$127.60
Purchase #4	$15.32	7.723%	$16.5032	$16.50	$16.50	$16.50
Purchase #5	$40.45	4.682%	$42.3439	$42.34	$42.35	$42.30
Purchase #6	$178.26	11.739%	$199.1859	$199.19	$199.20	$199.20
Purchase #7	$208.91	7.139%	$223.8241	$223.82	$223.80	$223.80
7 purchase totals =	$817.56		$897.9259	$897.92	$897.95	$897.90