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	$131.30	13.365%	$148.8482	$148.85	$148.85	$148.80
Purchase #2	$42.65	10.429%	$47.098	$47.10	$47.10	$47.10
Purchase #3	$233.36	4.269%	$243.3221	$243.32	$243.30	$243.30
Purchase #4	$90.77	12.218%	$101.8603	$101.86	$101.85	$101.90
Purchase #5	$237.26	9.336%	$259.4106	$259.41	$259.40	$259.40
Purchase #6	$45.57	4.248%	$47.5058	$47.51	$47.50	$47.50
Purchase #7	$41.65	5.125%	$43.7846	$43.78	$43.80	$43.80
7 purchase totals =	$822.56		$891.8296	$891.83	$891.80	$891.80