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	$122.53	13.867%	$139.5212	$139.52	$139.50	$139.50
Purchase #2	$177.98	10.342%	$196.3867	$196.39	$196.40	$196.40
Purchase #3	$221.79	3.281%	$229.0669	$229.07	$229.05	$229.10
Purchase #4	$174.85	5.467%	$184.409	$184.41	$184.40	$184.40
Purchase #5	$64.85	11.731%	$72.4576	$72.46	$72.45	$72.50
Purchase #6	$217.95	13.156%	$246.6235	$246.62	$246.60	$246.60
Purchase #7	$22.92	13.121%	$25.9273	$25.93	$25.95	$25.90
7 purchase totals =	$1,002.87		$1,094.3922	$1,094.40	$1,094.35	$1,094.40