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	$84.54	8.178%	$91.4537	$91.45	$91.45	$91.50
Purchase #2	$119.39	7.127%	$127.8989	$127.90	$127.90	$127.90
Purchase #3	$80.88	9.818%	$88.8208	$88.82	$88.80	$88.80
Purchase #4	$241.28	6.503%	$256.9704	$256.97	$256.95	$257.00
Purchase #5	$108.50	6.863%	$115.9464	$115.95	$115.95	$115.90
Purchase #6	$239.88	9.250%	$262.0689	$262.07	$262.05	$262.10
Purchase #7	$173.71	6.840%	$185.5918	$185.59	$185.60	$185.60
7 purchase totals =	$1,048.18		$1,128.7509	$1,128.75	$1,128.70	$1,128.80