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	$137.33	5.840%	$145.3501	$145.35	$145.35	$145.40
Purchase #2	$245.58	3.766%	$254.8285	$254.83	$254.85	$254.80
Purchase #3	$232.60	5.561%	$245.5349	$245.53	$245.55	$245.50
Purchase #4	$107.50	11.403%	$119.7582	$119.76	$119.75	$119.80
Purchase #5	$143.75	10.256%	$158.493	$158.49	$158.50	$158.50
Purchase #6	$84.37	6.138%	$89.5486	$89.55	$89.55	$89.50
Purchase #7	$108.79	8.106%	$117.6085	$117.61	$117.60	$117.60
7 purchase totals =	$1,059.92		$1,131.1218	$1,131.12	$1,131.15	$1,131.10