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	$40.82	9.118%	$44.542	$44.54	$44.55	$44.50
Purchase #2	$133.49	9.247%	$145.8338	$145.83	$145.85	$145.80
Purchase #3	$238.99	11.216%	$265.7951	$265.80	$265.80	$265.80
Purchase #4	$188.63	6.494%	$200.8796	$200.88	$200.90	$200.90
Purchase #5	$131.59	3.569%	$136.2864	$136.29	$136.30	$136.30
Purchase #6	$217.36	10.152%	$239.4264	$239.43	$239.45	$239.40
Purchase #7	$56.58	12.810%	$63.8279	$63.83	$63.85	$63.80
7 purchase totals =	$1,007.46		$1,096.5912	$1,096.60	$1,096.70	$1,096.50