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	$227.79	13.786%	$259.1931	$259.19	$259.20	$259.20
Purchase #2	$76.53	10.405%	$84.4929	$84.49	$84.50	$84.50
Purchase #3	$88.90	12.375%	$99.9014	$99.90	$99.90	$99.90
Purchase #4	$250.34	12.615%	$281.9204	$281.92	$281.90	$281.90
Purchase #5	$87.85	5.304%	$92.5096	$92.51	$92.50	$92.50
Purchase #6	$213.71	6.273%	$227.116	$227.12	$227.10	$227.10
Purchase #7	$239.80	6.354%	$255.0369	$255.04	$255.05	$255.00
7 purchase totals =	$1,184.92		$1,300.1703	$1,300.17	$1,300.15	$1,300.10