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	$89.35	5.867%	$94.5922	$94.59	$94.60	$94.60
Purchase #2	$124.57	3.214%	$128.5737	$128.57	$128.55	$128.60
Purchase #3	$222.33	7.579%	$239.1804	$239.18	$239.20	$239.20
Purchase #4	$81.60	10.798%	$90.4112	$90.41	$90.40	$90.40
Purchase #5	$214.33	6.172%	$227.5584	$227.56	$227.55	$227.60
Purchase #6	$148.59	13.211%	$168.2202	$168.22	$168.20	$168.20
Purchase #7	$66.86	5.181%	$70.324	$70.32	$70.30	$70.30
7 purchase totals =	$947.63		$1,018.8601	$1,018.85	$1,018.80	$1,018.90