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	$12.99	8.417%	$14.0834	$14.08	$14.10	$14.10
Purchase #2	$105.57	5.575%	$111.4555	$111.46	$111.45	$111.50
Purchase #3	$156.53	6.208%	$166.2474	$166.25	$166.25	$166.20
Purchase #4	$64.93	13.421%	$73.6443	$73.64	$73.65	$73.60
Purchase #5	$99.49	10.355%	$109.7922	$109.79	$109.80	$109.80
Purchase #6	$21.38	13.245%	$24.2118	$24.21	$24.20	$24.20
Purchase #7	$92.46	4.366%	$96.4968	$96.50	$96.50	$96.50
7 purchase totals =	$553.35		$595.9314	$595.93	$595.95	$595.90