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	$182.83	3.122%	$188.538	$188.54	$188.55	$188.50
Purchase #2	$48.37	6.821%	$51.6693	$51.67	$51.65	$51.70
Purchase #3	$88.69	11.828%	$99.1803	$99.18	$99.20	$99.20
Purchase #4	$107.54	3.218%	$111.0006	$111.00	$111.00	$111.00
Purchase #5	$49.95	13.871%	$56.8786	$56.88	$56.90	$56.90
Purchase #6	$46.84	4.451%	$48.9248	$48.92	$48.90	$48.90
Purchase #7	$118.70	10.377%	$131.0175	$131.02	$131.00	$131.00
7 purchase totals =	$642.92		$687.2091	$687.21	$687.20	$687.20