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	$27.39	7.781%	$29.5212	$29.52	$29.50	$29.50
Purchase #2	$230.89	12.558%	$259.8852	$259.89	$259.90	$259.90
Purchase #3	$23.59	3.573%	$24.4329	$24.43	$24.45	$24.40
Purchase #4	$68.45	4.819%	$71.7486	$71.75	$71.75	$71.70
Purchase #5	$68.62	7.256%	$73.5991	$73.60	$73.60	$73.60
Purchase #6	$104.72	11.869%	$117.1492	$117.15	$117.15	$117.10
Purchase #7	$135.35	12.200%	$151.8627	$151.86	$151.85	$151.90
7 purchase totals =	$659.01		$728.1989	$728.20	$728.20	$728.10