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	$245.70	10.502%	$271.5034	$271.50	$271.50	$271.50
Purchase #2	$34.35	11.839%	$38.4167	$38.42	$38.40	$38.40
Purchase #3	$6.82	9.774%	$7.4866	$7.49	$7.50	$7.50
Purchase #4	$249.68	12.324%	$280.4506	$280.45	$280.45	$280.50
Purchase #5	$122.86	3.652%	$127.3468	$127.35	$127.35	$127.30
Purchase #6	$132.42	4.132%	$137.8916	$137.89	$137.90	$137.90
Purchase #7	$104.89	6.552%	$111.7624	$111.76	$111.75	$111.80
7 purchase totals =	$896.72		$974.8581	$974.86	$974.85	$974.90