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	$126.71	12.839%	$142.9783	$142.98	$143.00	$143.00
Purchase #2	$235.97	10.676%	$261.1622	$261.16	$261.15	$261.20
Purchase #3	$52.30	7.556%	$56.2518	$56.25	$56.25	$56.30
Purchase #4	$213.90	5.857%	$226.4281	$226.43	$226.45	$226.40
Purchase #5	$144.67	7.428%	$155.4161	$155.42	$155.40	$155.40
Purchase #6	$88.78	12.273%	$99.676	$99.68	$99.70	$99.70
Purchase #7	$147.61	7.200%	$158.2379	$158.24	$158.25	$158.20
7 purchase totals =	$1,009.94		$1,100.1504	$1,100.16	$1,100.20	$1,100.20