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	$155.81	4.264%	$162.4537	$162.45	$162.45	$162.50
Purchase #2	$126.31	8.154%	$136.6093	$136.61	$136.60	$136.60
Purchase #3	$176.54	3.821%	$183.2856	$183.29	$183.30	$183.30
Purchase #4	$133.78	6.666%	$142.6978	$142.70	$142.70	$142.70
Purchase #5	$203.80	13.694%	$231.7084	$231.71	$231.70	$231.70
Purchase #6	$37.42	8.524%	$40.6097	$40.61	$40.60	$40.60
Purchase #7	$76.86	5.263%	$80.9051	$80.91	$80.90	$80.90
7 purchase totals =	$910.52		$978.2696	$978.28	$978.25	$978.30