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	$155.38	7.636%	$167.2448	$167.24	$167.25	$167.20
Purchase #2	$245.69	5.118%	$258.2644	$258.26	$258.25	$258.30
Purchase #3	$20.58	4.544%	$21.5152	$21.52	$21.50	$21.50
Purchase #4	$34.56	9.572%	$37.8681	$37.87	$37.85	$37.90
Purchase #5	$196.59	3.747%	$203.9562	$203.96	$203.95	$204.00
Purchase #6	$134.51	5.843%	$142.3694	$142.37	$142.35	$142.40
Purchase #7	$152.98	5.796%	$161.8467	$161.85	$161.85	$161.80
7 purchase totals =	$940.29		$993.0648	$993.07	$993.00	$993.10