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	$127.58	7.767%	$137.4891	$137.49	$137.50	$137.50
Purchase #2	$78.55	10.134%	$86.5103	$86.51	$86.50	$86.50
Purchase #3	$121.88	8.320%	$132.0204	$132.02	$132.00	$132.00
Purchase #4	$162.45	13.594%	$184.5335	$184.53	$184.55	$184.50
Purchase #5	$39.55	3.627%	$40.9845	$40.98	$41.00	$41.00
Purchase #6	$118.45	11.767%	$132.388	$132.39	$132.40	$132.40
Purchase #7	$152.97	7.415%	$164.3127	$164.31	$164.30	$164.30
7 purchase totals =	$801.43		$878.2385	$878.23	$878.25	$878.20