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	$46.49	10.796%	$51.5091	$51.51	$51.50	$51.50
Purchase #2	$137.32	5.252%	$144.532	$144.53	$144.55	$144.50
Purchase #3	$232.94	3.826%	$241.8523	$241.85	$241.85	$241.90
Purchase #4	$172.46	9.468%	$188.7885	$188.79	$188.80	$188.80
Purchase #5	$164.46	5.161%	$172.9478	$172.95	$172.95	$172.90
Purchase #6	$174.75	13.264%	$197.9288	$197.93	$197.95	$197.90
Purchase #7	$70.46	12.578%	$79.3225	$79.32	$79.30	$79.30
7 purchase totals =	$998.88		$1,076.8810	$1,076.88	$1,076.90	$1,076.80