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	$29.25	7.761%	$31.5201	$31.52	$31.50	$31.50
Purchase #2	$88.55	12.761%	$99.8499	$99.85	$99.85	$99.80
Purchase #3	$95.54	6.635%	$101.8791	$101.88	$101.90	$101.90
Purchase #4	$59.55	12.118%	$66.7663	$66.77	$66.75	$66.80
Purchase #5	$151.25	10.778%	$167.5517	$167.55	$167.55	$167.60
Purchase #6	$16.90	10.777%	$18.7213	$18.72	$18.70	$18.70
Purchase #7	$7.55	10.387%	$8.3342	$8.33	$8.35	$8.30
7 purchase totals =	$448.59		$494.6226	$494.62	$494.60	$494.60