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	$156.30	11.584%	$174.4058	$174.41	$174.40	$174.40
Purchase #2	$247.49	12.856%	$279.3073	$279.31	$279.30	$279.30
Purchase #3	$119.66	9.103%	$130.5526	$130.55	$130.55	$130.60
Purchase #4	$40.89	6.612%	$43.5936	$43.59	$43.60	$43.60
Purchase #5	$13.31	6.531%	$14.1793	$14.18	$14.20	$14.20
Purchase #6	$103.41	8.548%	$112.2495	$112.25	$112.25	$112.20
Purchase #7	$94.44	4.393%	$98.5887	$98.59	$98.60	$98.60
7 purchase totals =	$775.50		$852.8768	$852.88	$852.90	$852.90