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	$44.45	9.312%	$48.5892	$48.59	$48.60	$48.60
Purchase #2	$52.55	6.636%	$56.0372	$56.04	$56.05	$56.00
Purchase #3	$25.59	5.295%	$26.945	$26.95	$26.95	$26.90
Purchase #4	$60.75	4.631%	$63.5633	$63.56	$63.55	$63.60
Purchase #5	$185.31	4.624%	$193.8787	$193.88	$193.90	$193.90
Purchase #6	$78.32	13.698%	$89.0483	$89.05	$89.05	$89.00
Purchase #7	$158.85	13.597%	$180.4488	$180.45	$180.45	$180.40
7 purchase totals =	$605.82		$658.5105	$658.52	$658.55	$658.40