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	$18.26	9.746%	$20.0396	$20.04	$20.05	$20.00
Purchase #2	$27.25	12.296%	$30.6007	$30.60	$30.60	$30.60
Purchase #3	$146.48	12.801%	$165.2309	$165.23	$165.25	$165.20
Purchase #4	$143.97	3.789%	$149.425	$149.43	$149.45	$149.40
Purchase #5	$162.57	5.738%	$171.8983	$171.90	$171.90	$171.90
Purchase #6	$155.99	10.196%	$171.8947	$171.89	$171.90	$171.90
Purchase #7	$9.69	6.634%	$10.3328	$10.33	$10.35	$10.30
7 purchase totals =	$664.21		$719.4220	$719.42	$719.50	$719.30