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	$25.74	9.156%	$28.0968	$28.10	$28.10	$28.10
Purchase #2	$70.50	3.436%	$72.9224	$72.92	$72.90	$72.90
Purchase #3	$133.69	8.528%	$145.0911	$145.09	$145.10	$145.10
Purchase #4	$154.83	11.137%	$172.0734	$172.07	$172.05	$172.10
Purchase #5	$63.56	6.152%	$67.4702	$67.47	$67.45	$67.50
Purchase #6	$142.60	6.684%	$152.1314	$152.13	$152.15	$152.10
Purchase #7	$94.43	7.781%	$101.7776	$101.78	$101.80	$101.80
7 purchase totals =	$685.35		$739.5629	$739.56	$739.55	$739.60