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	$34.34	13.139%	$38.8519	$38.85	$38.85	$38.90
Purchase #2	$148.61	10.453%	$164.1442	$164.14	$164.15	$164.10
Purchase #3	$241.59	3.135%	$249.1638	$249.16	$249.15	$249.20
Purchase #4	$126.37	8.379%	$136.9585	$136.96	$136.95	$137.00
Purchase #5	$169.97	12.296%	$190.8695	$190.87	$190.85	$190.90
Purchase #6	$145.65	3.770%	$151.141	$151.14	$151.15	$151.10
Purchase #7	$84.75	6.225%	$90.0257	$90.03	$90.05	$90.00
7 purchase totals =	$951.28		$1,021.1546	$1,021.15	$1,021.15	$1,021.20