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	$71.91	13.458%	$81.5876	$81.59	$81.60	$81.60
Purchase #2	$38.52	10.649%	$42.622	$42.62	$42.60	$42.60
Purchase #3	$91.59	8.210%	$99.1095	$99.11	$99.10	$99.10
Purchase #4	$162.83	3.646%	$168.7668	$168.77	$168.75	$168.80
Purchase #5	$199.50	4.577%	$208.6311	$208.63	$208.65	$208.60
Purchase #6	$129.62	3.796%	$134.5404	$134.54	$134.55	$134.50
Purchase #7	$118.42	11.764%	$132.3509	$132.35	$132.35	$132.40
7 purchase totals =	$812.39		$867.6083	$867.61	$867.60	$867.60