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	$37.60	3.397%	$38.8773	$38.88	$38.90	$38.90
Purchase #2	$65.75	8.239%	$71.1671	$71.17	$71.15	$71.20
Purchase #3	$134.95	12.146%	$151.341	$151.34	$151.35	$151.30
Purchase #4	$85.71	9.525%	$93.8739	$93.87	$93.85	$93.90
Purchase #5	$227.42	6.268%	$241.6747	$241.67	$241.65	$241.70
Purchase #6	$179.62	3.523%	$185.948	$185.95	$185.95	$185.90
Purchase #7	$122.46	7.494%	$131.6372	$131.64	$131.65	$131.60
7 purchase totals =	$853.51		$914.5192	$914.52	$914.50	$914.50