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	$222.50	4.634%	$232.8107	$232.81	$232.80	$232.80
Purchase #2	$43.75	11.853%	$48.9357	$48.94	$48.95	$48.90
Purchase #3	$42.82	7.263%	$45.93	$45.93	$45.95	$45.90
Purchase #4	$70.93	10.569%	$78.4266	$78.43	$78.45	$78.40
Purchase #5	$196.94	8.755%	$214.1821	$214.18	$214.20	$214.20
Purchase #6	$89.93	13.530%	$102.0975	$102.10	$102.10	$102.10
Purchase #7	$63.40	6.650%	$67.6161	$67.62	$67.60	$67.60
7 purchase totals =	$730.27		$789.9987	$790.01	$790.05	$789.90