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	$104.98	11.811%	$117.3792	$117.38	$117.40	$117.40
Purchase #2	$73.26	13.867%	$83.419	$83.42	$83.40	$83.40
Purchase #3	$17.87	5.578%	$18.8668	$18.87	$18.85	$18.90
Purchase #4	$78.51	10.617%	$86.8454	$86.85	$86.85	$86.80
Purchase #5	$208.45	12.746%	$235.019	$235.02	$235.00	$235.00
Purchase #6	$82.85	9.572%	$90.7804	$90.78	$90.80	$90.80
Purchase #7	$65.69	4.159%	$68.422	$68.42	$68.40	$68.40
7 purchase totals =	$631.61		$700.7318	$700.74	$700.70	$700.70