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	$222.59	7.520%	$239.3288	$239.33	$239.35	$239.30
Purchase #2	$130.75	6.434%	$139.1625	$139.16	$139.15	$139.20
Purchase #3	$35.25	10.123%	$38.8184	$38.82	$38.80	$38.80
Purchase #4	$183.82	4.177%	$191.4982	$191.50	$191.50	$191.50
Purchase #5	$191.57	4.531%	$200.25	$200.25	$200.25	$200.30
Purchase #6	$13.86	3.156%	$14.2974	$14.30	$14.30	$14.30
Purchase #7	$71.82	13.451%	$81.4805	$81.48	$81.50	$81.50
7 purchase totals =	$849.66		$904.8358	$904.84	$904.85	$904.90