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	$163.31	13.473%	$185.3128	$185.31	$185.30	$185.30
Purchase #2	$220.38	9.752%	$241.8715	$241.87	$241.85	$241.90
Purchase #3	$157.65	13.859%	$179.4987	$179.50	$179.50	$179.50
Purchase #4	$76.45	6.127%	$81.1341	$81.13	$81.15	$81.10
Purchase #5	$14.32	4.768%	$15.0028	$15.00	$15.00	$15.00
Purchase #6	$134.93	4.268%	$140.6888	$140.69	$140.70	$140.70
Purchase #7	$43.55	7.505%	$46.8184	$46.82	$46.80	$46.80
7 purchase totals =	$810.59		$890.3271	$890.32	$890.30	$890.30