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	$11.44	7.874%	$12.3408	$12.34	$12.35	$12.30
Purchase #2	$126.57	13.717%	$143.9316	$143.93	$143.95	$143.90
Purchase #3	$143.47	10.724%	$158.8557	$158.86	$158.85	$158.90
Purchase #4	$148.68	10.743%	$164.6527	$164.65	$164.65	$164.70
Purchase #5	$30.42	12.167%	$34.1212	$34.12	$34.10	$34.10
Purchase #6	$209.37	7.121%	$224.2792	$224.28	$224.30	$224.30
Purchase #7	$77.83	5.547%	$82.1472	$82.15	$82.15	$82.10
7 purchase totals =	$747.78		$820.3284	$820.33	$820.35	$820.30