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	$27.88	5.677%	$29.4627	$29.46	$29.45	$29.50
Purchase #2	$174.40	10.429%	$192.5882	$192.59	$192.60	$192.60
Purchase #3	$229.42	5.637%	$242.3524	$242.35	$242.35	$242.40
Purchase #4	$36.59	11.270%	$40.7137	$40.71	$40.70	$40.70
Purchase #5	$53.57	10.541%	$59.2168	$59.22	$59.20	$59.20
Purchase #6	$143.47	3.659%	$148.7196	$148.72	$148.70	$148.70
Purchase #7	$204.35	7.351%	$219.3718	$219.37	$219.35	$219.40
7 purchase totals =	$869.68		$932.4252	$932.42	$932.35	$932.50