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	$31.73	12.182%	$35.5953	$35.60	$35.60	$35.60
Purchase #2	$206.83	5.586%	$218.3835	$218.38	$218.40	$218.40
Purchase #3	$241.29	9.858%	$265.0764	$265.08	$265.10	$265.10
Purchase #4	$106.84	4.611%	$111.7664	$111.77	$111.75	$111.80
Purchase #5	$118.62	10.724%	$131.3408	$131.34	$131.35	$131.30
Purchase #6	$81.41	9.860%	$89.437	$89.44	$89.45	$89.40
Purchase #7	$115.67	9.565%	$126.7338	$126.73	$126.75	$126.70
7 purchase totals =	$902.39		$978.3332	$978.34	$978.40	$978.30