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	$80.48	9.466%	$88.0982	$88.10	$88.10	$88.10
Purchase #2	$129.27	11.187%	$143.7314	$143.73	$143.75	$143.70
Purchase #3	$142.45	9.323%	$155.7306	$155.73	$155.75	$155.70
Purchase #4	$27.53	13.874%	$31.3495	$31.35	$31.35	$31.30
Purchase #5	$78.42	11.683%	$87.5818	$87.58	$87.60	$87.60
Purchase #6	$48.59	3.784%	$50.4286	$50.43	$50.45	$50.40
Purchase #7	$101.80	9.376%	$111.3448	$111.34	$111.35	$111.30
7 purchase totals =	$608.54		$668.2649	$668.26	$668.35	$668.10