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	$137.69	9.318%	$150.52	$150.52	$150.50	$150.50
Purchase #2	$76.53	4.770%	$80.1805	$80.18	$80.20	$80.20
Purchase #3	$99.27	3.523%	$102.7673	$102.77	$102.75	$102.80
Purchase #4	$218.58	13.143%	$247.308	$247.31	$247.30	$247.30
Purchase #5	$189.44	3.472%	$196.0174	$196.02	$196.00	$196.00
Purchase #6	$94.65	11.463%	$105.4997	$105.50	$105.50	$105.50
Purchase #7	$214.67	7.643%	$231.0772	$231.08	$231.10	$231.10
7 purchase totals =	$1,030.83		$1,113.3701	$1,113.38	$1,113.35	$1,113.40