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	$133.61	5.535%	$141.0053	$141.01	$141.00	$141.00
Purchase #2	$87.70	13.665%	$99.6842	$99.68	$99.70	$99.70
Purchase #3	$132.35	4.680%	$138.544	$138.54	$138.55	$138.50
Purchase #4	$197.37	5.506%	$208.2372	$208.24	$208.25	$208.20
Purchase #5	$236.90	10.304%	$261.3102	$261.31	$261.30	$261.30
Purchase #6	$74.77	8.692%	$81.269	$81.27	$81.25	$81.30
Purchase #7	$54.74	8.768%	$59.5396	$59.54	$59.55	$59.50
7 purchase totals =	$917.44		$989.5895	$989.59	$989.60	$989.50