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	$96.86	6.250%	$102.9138	$102.91	$102.90	$102.90
Purchase #2	$37.42	13.113%	$42.3269	$42.33	$42.35	$42.30
Purchase #3	$28.53	10.177%	$31.4335	$31.43	$31.45	$31.40
Purchase #4	$249.82	5.256%	$262.9505	$262.95	$262.95	$263.00
Purchase #5	$236.58	7.117%	$253.4174	$253.42	$253.40	$253.40
Purchase #6	$200.93	8.794%	$218.5998	$218.60	$218.60	$218.60
Purchase #7	$166.83	5.786%	$176.4828	$176.48	$176.50	$176.50
7 purchase totals =	$1,016.97		$1,088.1247	$1,088.12	$1,088.15	$1,088.10