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	$32.64	5.567%	$34.4571	$34.46	$34.45	$34.50
Purchase #2	$89.78	10.351%	$99.0731	$99.07	$99.05	$99.10
Purchase #3	$52.43	12.743%	$59.1112	$59.11	$59.10	$59.10
Purchase #4	$155.67	8.239%	$168.4957	$168.50	$168.50	$168.50
Purchase #5	$6.43	4.357%	$6.7102	$6.71	$6.70	$6.70
Purchase #6	$120.29	9.679%	$131.9329	$131.93	$131.95	$131.90
Purchase #7	$154.32	7.305%	$165.5931	$165.59	$165.60	$165.60
7 purchase totals =	$611.56		$665.3733	$665.37	$665.35	$665.40