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	$38.42	11.664%	$42.9013	$42.90	$42.90	$42.90
Purchase #2	$207.66	5.574%	$219.235	$219.24	$219.25	$219.20
Purchase #3	$39.39	3.551%	$40.7887	$40.79	$40.80	$40.80
Purchase #4	$156.47	11.386%	$174.2857	$174.29	$174.30	$174.30
Purchase #5	$216.81	11.260%	$241.2228	$241.22	$241.20	$241.20
Purchase #6	$233.65	10.523%	$258.237	$258.24	$258.25	$258.20
Purchase #7	$160.64	4.249%	$167.4656	$167.47	$167.45	$167.50
7 purchase totals =	$1,053.04		$1,144.1361	$1,144.15	$1,144.15	$1,144.10