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	$141.39	12.268%	$158.7357	$158.74	$158.75	$158.70
Purchase #2	$80.93	10.205%	$89.1889	$89.19	$89.20	$89.20
Purchase #3	$172.50	7.378%	$185.2271	$185.23	$185.25	$185.20
Purchase #4	$95.31	7.146%	$102.1209	$102.12	$102.10	$102.10
Purchase #5	$127.95	12.782%	$144.3046	$144.30	$144.30	$144.30
Purchase #6	$99.25	8.590%	$107.7756	$107.78	$107.80	$107.80
Purchase #7	$120.50	4.864%	$126.3611	$126.36	$126.35	$126.40
7 purchase totals =	$837.83		$913.7139	$913.72	$913.75	$913.70