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	$40.28	12.738%	$45.4109	$45.41	$45.40	$45.40
Purchase #2	$48.48	8.295%	$52.5014	$52.50	$52.50	$52.50
Purchase #3	$142.34	4.385%	$148.5816	$148.58	$148.60	$148.60
Purchase #4	$163.26	13.466%	$185.2446	$185.24	$185.25	$185.20
Purchase #5	$154.48	6.360%	$164.3049	$164.30	$164.30	$164.30
Purchase #6	$128.96	9.869%	$141.6871	$141.69	$141.70	$141.70
Purchase #7	$45.88	6.140%	$48.697	$48.70	$48.70	$48.70
7 purchase totals =	$723.68		$786.4275	$786.42	$786.45	$786.40