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	$22.31	9.803%	$24.497	$24.50	$24.50	$24.50
Purchase #2	$216.61	8.770%	$235.6067	$235.61	$235.60	$235.60
Purchase #3	$187.90	11.154%	$208.8584	$208.86	$208.85	$208.90
Purchase #4	$241.83	4.315%	$252.265	$252.27	$252.25	$252.30
Purchase #5	$86.57	3.213%	$89.3515	$89.35	$89.35	$89.40
Purchase #6	$61.42	6.754%	$65.5683	$65.57	$65.55	$65.60
Purchase #7	$109.74	5.840%	$116.1488	$116.15	$116.15	$116.10
7 purchase totals =	$926.38		$992.2957	$992.31	$992.25	$992.40