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	$27.86	6.754%	$29.7417	$29.74	$29.75	$29.70
Purchase #2	$230.93	8.811%	$251.2772	$251.28	$251.30	$251.30
Purchase #3	$136.92	5.625%	$144.6218	$144.62	$144.60	$144.60
Purchase #4	$80.31	11.473%	$89.524	$89.52	$89.50	$89.50
Purchase #5	$248.63	8.326%	$269.3309	$269.33	$269.35	$269.30
Purchase #6	$21.38	13.242%	$24.2111	$24.21	$24.20	$24.20
Purchase #7	$85.45	4.846%	$89.5909	$89.59	$89.60	$89.60
7 purchase totals =	$831.48		$898.2976	$898.29	$898.30	$898.20