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	$234.99	11.299%	$261.5415	$261.54	$261.55	$261.50
Purchase #2	$70.55	10.565%	$78.0036	$78.00	$78.00	$78.00
Purchase #3	$118.84	6.523%	$126.5919	$126.59	$126.60	$126.60
Purchase #4	$136.63	6.537%	$145.5615	$145.56	$145.55	$145.60
Purchase #5	$134.82	11.842%	$150.7854	$150.79	$150.80	$150.80
Purchase #6	$97.41	4.601%	$101.8918	$101.89	$101.90	$101.90
Purchase #7	$35.57	7.210%	$38.1346	$38.13	$38.15	$38.10
7 purchase totals =	$828.81		$902.5103	$902.50	$902.55	$902.50