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	$131.91	11.547%	$147.1416	$147.14	$147.15	$147.10
Purchase #2	$233.38	12.631%	$262.8582	$262.86	$262.85	$262.90
Purchase #3	$126.83	8.706%	$137.8718	$137.87	$137.85	$137.90
Purchase #4	$22.86	10.757%	$25.3191	$25.32	$25.30	$25.30
Purchase #5	$141.36	3.772%	$146.6921	$146.69	$146.70	$146.70
Purchase #6	$14.64	4.613%	$15.3153	$15.32	$15.30	$15.30
Purchase #7	$236.94	7.664%	$255.0991	$255.10	$255.10	$255.10
7 purchase totals =	$907.92		$990.2972	$990.30	$990.25	$990.30