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	$51.78	5.262%	$54.5047	$54.50	$54.50	$54.50
Purchase #2	$36.73	4.204%	$38.2741	$38.27	$38.25	$38.30
Purchase #3	$99.34	8.837%	$108.1187	$108.12	$108.10	$108.10
Purchase #4	$164.88	12.750%	$185.9022	$185.90	$185.90	$185.90
Purchase #5	$181.82	10.299%	$200.5456	$200.55	$200.55	$200.50
Purchase #6	$24.28	5.839%	$25.6977	$25.70	$25.70	$25.70
Purchase #7	$50.64	9.838%	$55.622	$55.62	$55.60	$55.60
7 purchase totals =	$609.47		$668.6650	$668.66	$668.60	$668.60