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	$230.78	12.529%	$259.6944	$259.69	$259.70	$259.70
Purchase #2	$26.37	13.119%	$29.8295	$29.83	$29.85	$29.80
Purchase #3	$34.91	10.202%	$38.4715	$38.47	$38.45	$38.50
Purchase #4	$198.58	6.780%	$212.0437	$212.04	$212.05	$212.00
Purchase #5	$66.41	7.267%	$71.236	$71.24	$71.25	$71.20
Purchase #6	$116.70	5.874%	$123.555	$123.56	$123.55	$123.60
Purchase #7	$224.57	8.489%	$243.6337	$243.63	$243.65	$243.60
7 purchase totals =	$898.32		$978.4638	$978.46	$978.50	$978.40