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	$78.73	4.521%	$82.2894	$82.29	$82.30	$82.30
Purchase #2	$125.34	6.857%	$133.9346	$133.93	$133.95	$133.90
Purchase #3	$57.25	7.431%	$61.5042	$61.50	$61.50	$61.50
Purchase #4	$232.32	4.222%	$242.1286	$242.13	$242.15	$242.10
Purchase #5	$61.86	13.151%	$69.9952	$70.00	$70.00	$70.00
Purchase #6	$45.43	13.168%	$51.4122	$51.41	$51.40	$51.40
Purchase #7	$248.60	4.776%	$260.4731	$260.47	$260.45	$260.50
7 purchase totals =	$849.53		$901.7373	$901.73	$901.75	$901.70