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	$220.38	8.728%	$239.6148	$239.61	$239.60	$239.60
Purchase #2	$249.43	12.488%	$280.5788	$280.58	$280.60	$280.60
Purchase #3	$216.70	9.650%	$237.6116	$237.61	$237.60	$237.60
Purchase #4	$131.88	7.334%	$141.5521	$141.55	$141.55	$141.60
Purchase #5	$42.60	7.675%	$45.8696	$45.87	$45.85	$45.90
Purchase #6	$149.81	9.373%	$163.8517	$163.85	$163.85	$163.90
Purchase #7	$127.61	10.848%	$141.4531	$141.45	$141.45	$141.50
7 purchase totals =	$1,138.41		$1,250.5317	$1,250.52	$1,250.50	$1,250.70