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	$71.47	12.487%	$80.3945	$80.39	$80.40	$80.40
Purchase #2	$212.37	6.102%	$225.3288	$225.33	$225.35	$225.30
Purchase #3	$226.76	3.312%	$234.2703	$234.27	$234.25	$234.30
Purchase #4	$119.87	6.576%	$127.7527	$127.75	$127.75	$127.80
Purchase #5	$102.34	13.498%	$116.1539	$116.15	$116.15	$116.20
Purchase #6	$76.47	9.202%	$83.5068	$83.51	$83.50	$83.50
Purchase #7	$158.77	9.342%	$173.6023	$173.60	$173.60	$173.60
7 purchase totals =	$968.05		$1,041.0093	$1,041.00	$1,041.00	$1,041.10