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	$29.51	5.515%	$31.1375	$31.14	$31.15	$31.10
Purchase #2	$111.65	3.393%	$115.4383	$115.44	$115.45	$115.40
Purchase #3	$40.61	6.719%	$43.3386	$43.34	$43.35	$43.30
Purchase #4	$221.82	7.126%	$237.6269	$237.63	$237.65	$237.60
Purchase #5	$196.93	9.821%	$216.2705	$216.27	$216.25	$216.30
Purchase #6	$157.93	4.149%	$164.4825	$164.48	$164.50	$164.50
Purchase #7	$140.37	11.311%	$156.2473	$156.25	$156.25	$156.20
7 purchase totals =	$898.82		$964.5416	$964.55	$964.60	$964.40