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	$241.83	12.153%	$271.2196	$271.22	$271.20	$271.20
Purchase #2	$155.34	13.575%	$176.4274	$176.43	$176.45	$176.40
Purchase #3	$32.47	3.801%	$33.7042	$33.70	$33.70	$33.70
Purchase #4	$126.73	12.303%	$142.3216	$142.32	$142.30	$142.30
Purchase #5	$194.91	6.596%	$207.7663	$207.77	$207.75	$207.80
Purchase #6	$135.69	3.133%	$139.9412	$139.94	$139.95	$139.90
Purchase #7	$78.25	8.808%	$85.1423	$85.14	$85.15	$85.10
7 purchase totals =	$965.22		$1,056.5226	$1,056.52	$1,056.50	$1,056.40