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	$184.37	10.302%	$203.3638	$203.36	$203.35	$203.40
Purchase #2	$137.82	9.263%	$150.5863	$150.59	$150.60	$150.60
Purchase #3	$159.81	3.648%	$165.6399	$165.64	$165.65	$165.60
Purchase #4	$227.62	5.644%	$240.4669	$240.47	$240.45	$240.50
Purchase #5	$116.46	6.431%	$123.9495	$123.95	$123.95	$123.90
Purchase #6	$44.61	3.713%	$46.2664	$46.27	$46.25	$46.30
Purchase #7	$9.46	8.110%	$10.2272	$10.23	$10.25	$10.20
7 purchase totals =	$880.15		$940.5000	$940.51	$940.50	$940.50