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	$113.98	12.699%	$128.4543	$128.45	$128.45	$128.50
Purchase #2	$47.33	5.536%	$49.9502	$49.95	$49.95	$50.00
Purchase #3	$43.41	9.413%	$47.4962	$47.50	$47.50	$47.50
Purchase #4	$114.59	4.243%	$119.4521	$119.45	$119.45	$119.50
Purchase #5	$69.26	13.116%	$78.3441	$78.34	$78.35	$78.30
Purchase #6	$106.82	11.505%	$119.1096	$119.11	$119.10	$119.10
Purchase #7	$41.92	3.136%	$43.2346	$43.23	$43.25	$43.20
7 purchase totals =	$537.31		$586.0411	$586.03	$586.05	$586.10