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	$82.53	8.436%	$89.4922	$89.49	$89.50	$89.50
Purchase #2	$49.61	10.349%	$54.7441	$54.74	$54.75	$54.70
Purchase #3	$47.83	3.197%	$49.3591	$49.36	$49.35	$49.40
Purchase #4	$157.71	11.106%	$175.2253	$175.23	$175.25	$175.20
Purchase #5	$58.47	6.440%	$62.2355	$62.24	$62.25	$62.20
Purchase #6	$123.99	6.427%	$131.9588	$131.96	$131.95	$132.00
Purchase #7	$32.88	4.851%	$34.475	$34.48	$34.50	$34.50
7 purchase totals =	$553.02		$597.4900	$597.50	$597.55	$597.50