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	$16.96	13.181%	$19.1955	$19.20	$19.20	$19.20
Purchase #2	$81.35	9.564%	$89.1303	$89.13	$89.15	$89.10
Purchase #3	$120.67	4.602%	$126.2232	$126.22	$126.20	$126.20
Purchase #4	$41.56	4.207%	$43.3084	$43.31	$43.30	$43.30
Purchase #5	$124.77	13.655%	$141.8073	$141.81	$141.80	$141.80
Purchase #6	$46.25	13.184%	$52.3476	$52.35	$52.35	$52.30
Purchase #7	$50.53	11.430%	$56.3056	$56.31	$56.30	$56.30
7 purchase totals =	$482.09		$528.3179	$528.33	$528.30	$528.20