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	$94.97	4.498%	$99.2418	$99.24	$99.25	$99.20
Purchase #2	$160.56	13.821%	$182.751	$182.75	$182.75	$182.80
Purchase #3	$168.80	6.733%	$180.1653	$180.17	$180.15	$180.20
Purchase #4	$39.42	11.334%	$43.8879	$43.89	$43.90	$43.90
Purchase #5	$59.70	3.741%	$61.9334	$61.93	$61.95	$61.90
Purchase #6	$37.84	3.456%	$39.1478	$39.15	$39.15	$39.10
Purchase #7	$143.64	10.354%	$158.5125	$158.51	$158.50	$158.50
7 purchase totals =	$704.93		$765.6397	$765.64	$765.65	$765.60