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	$39.88	8.401%	$43.2303	$43.23	$43.25	$43.20
Purchase #2	$144.82	11.415%	$161.3512	$161.35	$161.35	$161.40
Purchase #3	$48.74	9.174%	$53.2114	$53.21	$53.20	$53.20
Purchase #4	$205.73	9.681%	$225.6467	$225.65	$225.65	$225.60
Purchase #5	$155.88	11.735%	$174.1725	$174.17	$174.15	$174.20
Purchase #6	$63.77	13.622%	$72.4567	$72.46	$72.45	$72.50
Purchase #7	$225.31	6.443%	$239.8267	$239.83	$239.85	$239.80
7 purchase totals =	$884.13		$969.8955	$969.90	$969.90	$969.90