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	$213.49	11.629%	$238.3168	$238.32	$238.30	$238.30
Purchase #2	$70.83	10.718%	$78.4216	$78.42	$78.40	$78.40
Purchase #3	$171.53	12.843%	$193.5596	$193.56	$193.55	$193.60
Purchase #4	$103.74	12.237%	$116.4347	$116.43	$116.45	$116.40
Purchase #5	$118.25	12.323%	$132.8219	$132.82	$132.80	$132.80
Purchase #6	$80.36	13.671%	$91.346	$91.35	$91.35	$91.30
Purchase #7	$119.74	10.871%	$132.7569	$132.76	$132.75	$132.80
7 purchase totals =	$877.94		$983.6575	$983.66	$983.60	$983.60