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	$243.51	12.716%	$274.4747	$274.47	$274.45	$274.50
Purchase #2	$62.91	13.742%	$71.5551	$71.56	$71.55	$71.60
Purchase #3	$52.37	8.705%	$56.9288	$56.93	$56.95	$56.90
Purchase #4	$173.35	3.106%	$178.7343	$178.73	$178.75	$178.70
Purchase #5	$166.65	13.103%	$188.4861	$188.49	$188.50	$188.50
Purchase #6	$105.64	10.792%	$117.0407	$117.04	$117.05	$117.00
Purchase #7	$101.51	11.238%	$112.9177	$112.92	$112.90	$112.90
7 purchase totals =	$905.94		$1,000.1374	$1,000.14	$1,000.15	$1,000.10