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	$165.76	6.436%	$176.4283	$176.43	$176.45	$176.40
Purchase #2	$173.65	5.492%	$183.1869	$183.19	$183.20	$183.20
Purchase #3	$33.68	9.382%	$36.8399	$36.84	$36.85	$36.80
Purchase #4	$49.69	9.824%	$54.5715	$54.57	$54.55	$54.60
Purchase #5	$105.36	3.796%	$109.3595	$109.36	$109.35	$109.40
Purchase #6	$90.47	10.379%	$99.8599	$99.86	$99.85	$99.90
Purchase #7	$243.69	4.632%	$254.9777	$254.98	$255.00	$255.00
7 purchase totals =	$862.30		$915.2237	$915.23	$915.25	$915.30