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	$24.54	12.265%	$27.5498	$27.55	$27.55	$27.50
Purchase #2	$37.55	7.769%	$40.4673	$40.47	$40.45	$40.50
Purchase #3	$155.90	13.343%	$176.7017	$176.70	$176.70	$176.70
Purchase #4	$116.35	10.556%	$128.6319	$128.63	$128.65	$128.60
Purchase #5	$231.72	10.865%	$256.8964	$256.90	$256.90	$256.90
Purchase #6	$144.37	7.788%	$155.6135	$155.61	$155.60	$155.60
Purchase #7	$84.84	7.249%	$90.9901	$90.99	$91.00	$91.00
7 purchase totals =	$795.27		$876.8507	$876.85	$876.85	$876.80