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	$101.93	12.353%	$114.5214	$114.52	$114.50	$114.50
Purchase #2	$83.71	7.865%	$90.2938	$90.29	$90.30	$90.30
Purchase #3	$76.25	8.437%	$82.6832	$82.68	$82.70	$82.70
Purchase #4	$248.85	13.306%	$281.962	$281.96	$281.95	$282.00
Purchase #5	$14.71	8.417%	$15.9481	$15.95	$15.95	$15.90
Purchase #6	$137.42	10.314%	$151.5935	$151.59	$151.60	$151.60
Purchase #7	$9.81	11.837%	$10.9712	$10.97	$10.95	$11.00
7 purchase totals =	$672.68		$747.9732	$747.96	$747.95	$748.00