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	$38.96	6.837%	$41.6237	$41.62	$41.60	$41.60
Purchase #2	$98.83	12.382%	$111.0671	$111.07	$111.05	$111.10
Purchase #3	$155.37	7.627%	$167.2201	$167.22	$167.20	$167.20
Purchase #4	$104.46	6.612%	$111.3669	$111.37	$111.35	$111.40
Purchase #5	$250.94	7.450%	$269.635	$269.64	$269.65	$269.60
Purchase #6	$26.52	7.557%	$28.5241	$28.52	$28.50	$28.50
Purchase #7	$129.54	5.608%	$136.8046	$136.80	$136.80	$136.80
7 purchase totals =	$804.62		$866.2415	$866.24	$866.15	$866.20