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	$248.64	11.752%	$277.8602	$277.86	$277.85	$277.90
Purchase #2	$192.59	10.336%	$212.4961	$212.50	$212.50	$212.50
Purchase #3	$186.92	13.123%	$211.4495	$211.45	$211.45	$211.40
Purchase #4	$168.75	13.357%	$191.2899	$191.29	$191.30	$191.30
Purchase #5	$125.88	11.867%	$140.8182	$140.82	$140.80	$140.80
Purchase #6	$118.64	4.365%	$123.8186	$123.82	$123.80	$123.80
Purchase #7	$96.46	6.381%	$102.6151	$102.62	$102.60	$102.60
7 purchase totals =	$1,137.88		$1,260.3476	$1,260.36	$1,260.30	$1,260.30