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	$180.89	9.739%	$198.5069	$198.51	$198.50	$198.50
Purchase #2	$126.85	3.370%	$131.1248	$131.12	$131.10	$131.10
Purchase #3	$248.81	11.167%	$276.5946	$276.59	$276.60	$276.60
Purchase #4	$150.30	13.836%	$171.0955	$171.10	$171.10	$171.10
Purchase #5	$15.55	10.505%	$17.1835	$17.18	$17.20	$17.20
Purchase #6	$103.58	5.826%	$109.6146	$109.61	$109.60	$109.60
Purchase #7	$133.87	3.648%	$138.7536	$138.75	$138.75	$138.80
7 purchase totals =	$959.85		$1,042.8735	$1,042.86	$1,042.85	$1,042.90