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	$111.46	6.216%	$118.3884	$118.39	$118.40	$118.40
Purchase #2	$182.29	8.619%	$198.0016	$198.00	$198.00	$198.00
Purchase #3	$111.61	13.361%	$126.5222	$126.52	$126.50	$126.50
Purchase #4	$61.76	5.597%	$65.2167	$65.22	$65.20	$65.20
Purchase #5	$226.29	12.784%	$255.2189	$255.22	$255.20	$255.20
Purchase #6	$158.91	8.736%	$172.7924	$172.79	$172.80	$172.80
Purchase #7	$102.47	9.380%	$112.0817	$112.08	$112.10	$112.10
7 purchase totals =	$954.79		$1,048.2219	$1,048.22	$1,048.20	$1,048.20