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	$213.89	12.470%	$240.5621	$240.56	$240.55	$240.60
Purchase #2	$93.89	5.593%	$99.1413	$99.14	$99.15	$99.10
Purchase #3	$216.69	4.784%	$227.0564	$227.06	$227.05	$227.10
Purchase #4	$96.67	13.372%	$109.5967	$109.60	$109.60	$109.60
Purchase #5	$248.61	10.563%	$274.8707	$274.87	$274.85	$274.90
Purchase #6	$244.77	13.666%	$278.2203	$278.22	$278.20	$278.20
Purchase #7	$81.66	10.671%	$90.3739	$90.37	$90.35	$90.40
7 purchase totals =	$1,196.18		$1,319.8214	$1,319.82	$1,319.75	$1,319.90