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	$50.74	10.173%	$55.9018	$55.90	$55.90	$55.90
Purchase #2	$38.28	13.746%	$43.542	$43.54	$43.55	$43.50
Purchase #3	$5.51	12.103%	$6.1769	$6.18	$6.20	$6.20
Purchase #4	$11.74	4.865%	$12.3112	$12.31	$12.30	$12.30
Purchase #5	$123.31	12.261%	$138.429	$138.43	$138.45	$138.40
Purchase #6	$199.72	7.725%	$215.1484	$215.15	$215.15	$215.10
Purchase #7	$201.82	10.320%	$222.6478	$222.65	$222.65	$222.60
7 purchase totals =	$631.12		$694.1571	$694.16	$694.20	$694.00