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	$246.79	4.614%	$258.1769	$258.18	$258.20	$258.20
Purchase #2	$96.64	7.772%	$104.1509	$104.15	$104.15	$104.20
Purchase #3	$233.63	13.690%	$265.6139	$265.61	$265.60	$265.60
Purchase #4	$56.78	11.860%	$63.5141	$63.51	$63.50	$63.50
Purchase #5	$128.88	5.832%	$136.3963	$136.40	$136.40	$136.40
Purchase #6	$127.48	13.239%	$144.3571	$144.36	$144.35	$144.40
Purchase #7	$27.78	12.635%	$31.29	$31.29	$31.30	$31.30
7 purchase totals =	$917.98		$1,003.4992	$1,003.50	$1,003.50	$1,003.60