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	$166.54	6.645%	$177.6066	$177.61	$177.60	$177.60
Purchase #2	$225.34	9.558%	$246.878	$246.88	$246.90	$246.90
Purchase #3	$38.85	5.436%	$40.9619	$40.96	$40.95	$41.00
Purchase #4	$72.30	8.429%	$78.3942	$78.39	$78.40	$78.40
Purchase #5	$124.65	9.574%	$136.584	$136.58	$136.60	$136.60
Purchase #6	$177.51	7.377%	$190.6049	$190.60	$190.60	$190.60
Purchase #7	$98.78	8.333%	$107.0113	$107.01	$107.00	$107.00
7 purchase totals =	$903.97		$978.0409	$978.03	$978.05	$978.10