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	$29.79	4.579%	$31.1541	$31.15	$31.15	$31.20
Purchase #2	$244.56	11.724%	$273.2322	$273.23	$273.25	$273.20
Purchase #3	$57.85	5.602%	$61.0908	$61.09	$61.10	$61.10
Purchase #4	$145.77	11.401%	$162.3892	$162.39	$162.40	$162.40
Purchase #5	$29.32	13.234%	$33.2002	$33.20	$33.20	$33.20
Purchase #6	$159.46	6.509%	$169.8393	$169.84	$169.85	$169.80
Purchase #7	$38.68	5.484%	$40.8012	$40.80	$40.80	$40.80
7 purchase totals =	$705.43		$771.7070	$771.70	$771.75	$771.70