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	$19.69	11.873%	$22.0278	$22.03	$22.05	$22.00
Purchase #2	$155.97	5.637%	$164.762	$164.76	$164.75	$164.80
Purchase #3	$13.49	12.223%	$15.1389	$15.14	$15.15	$15.10
Purchase #4	$116.34	9.844%	$127.7925	$127.79	$127.80	$127.80
Purchase #5	$132.94	13.539%	$150.9387	$150.94	$150.95	$150.90
Purchase #6	$95.31	5.292%	$100.3538	$100.35	$100.35	$100.40
Purchase #7	$72.67	10.498%	$80.2989	$80.30	$80.30	$80.30
7 purchase totals =	$606.41		$661.3126	$661.31	$661.35	$661.30