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	$112.83	13.192%	$127.7145	$127.71	$127.70	$127.70
Purchase #2	$126.50	5.311%	$133.2184	$133.22	$133.20	$133.20
Purchase #3	$141.48	7.354%	$151.8844	$151.88	$151.90	$151.90
Purchase #4	$239.36	10.872%	$265.3832	$265.38	$265.40	$265.40
Purchase #5	$136.36	3.784%	$141.5199	$141.52	$141.50	$141.50
Purchase #6	$232.90	6.609%	$248.2924	$248.29	$248.30	$248.30
Purchase #7	$9.64	8.458%	$10.4554	$10.46	$10.45	$10.50
7 purchase totals =	$999.07		$1,078.4682	$1,078.46	$1,078.45	$1,078.50