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	$120.89	13.508%	$137.2198	$137.22	$137.20	$137.20
Purchase #2	$213.33	13.307%	$241.7178	$241.72	$241.70	$241.70
Purchase #3	$184.34	6.506%	$196.3332	$196.33	$196.35	$196.30
Purchase #4	$15.89	9.184%	$17.3493	$17.35	$17.35	$17.30
Purchase #5	$91.61	11.455%	$102.1039	$102.10	$102.10	$102.10
Purchase #6	$92.75	13.448%	$105.223	$105.22	$105.20	$105.20
Purchase #7	$11.32	12.592%	$12.7454	$12.75	$12.75	$12.70
7 purchase totals =	$730.13		$812.6924	$812.69	$812.65	$812.50