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	$232.36	12.280%	$260.8938	$260.89	$260.90	$260.90
Purchase #2	$9.48	5.400%	$9.9919	$9.99	$10.00	$10.00
Purchase #3	$246.33	5.365%	$259.5456	$259.55	$259.55	$259.50
Purchase #4	$94.79	9.634%	$103.9221	$103.92	$103.90	$103.90
Purchase #5	$119.88	6.167%	$127.273	$127.27	$127.25	$127.30
Purchase #6	$248.29	3.265%	$256.3967	$256.40	$256.40	$256.40
Purchase #7	$100.99	4.835%	$105.8729	$105.87	$105.85	$105.90
7 purchase totals =	$1,052.12		$1,123.8960	$1,123.89	$1,123.85	$1,123.90