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	$138.98	6.650%	$148.2222	$148.22	$148.20	$148.20
Purchase #2	$83.60	13.492%	$94.8793	$94.88	$94.90	$94.90
Purchase #3	$243.56	12.750%	$274.6139	$274.61	$274.60	$274.60
Purchase #4	$75.76	4.203%	$78.9442	$78.94	$78.95	$78.90
Purchase #5	$99.30	12.752%	$111.9627	$111.96	$111.95	$112.00
Purchase #6	$226.35	13.432%	$256.7533	$256.75	$256.75	$256.80
Purchase #7	$62.40	3.600%	$64.6464	$64.65	$64.65	$64.60
7 purchase totals =	$929.95		$1,030.0220	$1,030.01	$1,030.00	$1,030.00