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	$166.80	10.317%	$184.0088	$184.01	$184.00	$184.00
Purchase #2	$215.67	9.659%	$236.5016	$236.50	$236.50	$236.50
Purchase #3	$134.94	11.768%	$150.8197	$150.82	$150.80	$150.80
Purchase #4	$137.81	9.106%	$150.359	$150.36	$150.35	$150.40
Purchase #5	$74.38	6.123%	$78.9343	$78.93	$78.95	$78.90
Purchase #6	$34.51	8.761%	$37.5334	$37.53	$37.55	$37.50
Purchase #7	$147.72	4.565%	$154.4634	$154.46	$154.45	$154.50
7 purchase totals =	$911.83		$992.6202	$992.61	$992.60	$992.60