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	$184.51	8.426%	$200.0568	$200.06	$200.05	$200.10
Purchase #2	$246.93	11.158%	$274.4824	$274.48	$274.50	$274.50
Purchase #3	$36.31	12.813%	$40.9624	$40.96	$40.95	$41.00
Purchase #4	$30.51	12.244%	$34.2456	$34.25	$34.25	$34.20
Purchase #5	$123.70	3.166%	$127.6163	$127.62	$127.60	$127.60
Purchase #6	$119.65	9.866%	$131.4547	$131.45	$131.45	$131.50
Purchase #7	$36.55	10.337%	$40.3282	$40.33	$40.35	$40.30
7 purchase totals =	$778.16		$849.1464	$849.15	$849.15	$849.20