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	$244.61	9.281%	$267.3123	$267.31	$267.30	$267.30
Purchase #2	$176.59	5.283%	$185.9192	$185.92	$185.90	$185.90
Purchase #3	$206.98	7.604%	$222.7188	$222.72	$222.70	$222.70
Purchase #4	$10.31	12.695%	$11.6189	$11.62	$11.60	$11.60
Purchase #5	$92.55	11.403%	$103.1035	$103.10	$103.10	$103.10
Purchase #6	$126.87	7.665%	$136.5946	$136.59	$136.60	$136.60
Purchase #7	$60.43	10.103%	$66.5352	$66.54	$66.55	$66.50
7 purchase totals =	$918.34		$993.8025	$993.80	$993.75	$993.70