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	$98.78	8.202%	$106.8819	$106.88	$106.90	$106.90
Purchase #2	$134.69	4.837%	$141.205	$141.21	$141.20	$141.20
Purchase #3	$229.50	11.592%	$256.1036	$256.10	$256.10	$256.10
Purchase #4	$146.29	6.677%	$156.0578	$156.06	$156.05	$156.10
Purchase #5	$62.66	4.191%	$65.2861	$65.29	$65.30	$65.30
Purchase #6	$17.53	10.579%	$19.3845	$19.38	$19.40	$19.40
Purchase #7	$144.38	7.691%	$155.4843	$155.48	$155.50	$155.50
7 purchase totals =	$833.83		$900.4032	$900.40	$900.45	$900.50