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	$231.55	9.633%	$253.8552	$253.86	$253.85	$253.90
Purchase #2	$159.88	4.687%	$167.3736	$167.37	$167.35	$167.40
Purchase #3	$39.86	8.144%	$43.1062	$43.11	$43.10	$43.10
Purchase #4	$167.31	10.670%	$185.162	$185.16	$185.15	$185.20
Purchase #5	$11.51	13.310%	$13.042	$13.04	$13.05	$13.00
Purchase #6	$58.79	4.493%	$61.4314	$61.43	$61.45	$61.40
Purchase #7	$105.90	8.565%	$114.9703	$114.97	$114.95	$115.00
7 purchase totals =	$774.80		$838.9407	$838.94	$838.90	$839.00