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	$248.67	11.738%	$277.8589	$277.86	$277.85	$277.90
Purchase #2	$116.75	9.554%	$127.9043	$127.90	$127.90	$127.90
Purchase #3	$151.38	11.583%	$168.9143	$168.91	$168.90	$168.90
Purchase #4	$126.99	13.857%	$144.587	$144.59	$144.60	$144.60
Purchase #5	$30.84	6.625%	$32.8832	$32.88	$32.90	$32.90
Purchase #6	$36.55	8.252%	$39.5661	$39.57	$39.55	$39.60
Purchase #7	$68.75	12.184%	$77.1265	$77.13	$77.15	$77.10
7 purchase totals =	$779.93		$868.8403	$868.84	$868.85	$868.90