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	$38.50	3.663%	$39.9103	$39.91	$39.90	$39.90
Purchase #2	$81.96	8.856%	$89.2184	$89.22	$89.20	$89.20
Purchase #3	$157.61	7.208%	$168.9705	$168.97	$168.95	$169.00
Purchase #4	$150.59	12.133%	$168.8611	$168.86	$168.85	$168.90
Purchase #5	$49.88	13.509%	$56.6183	$56.62	$56.60	$56.60
Purchase #6	$207.76	13.839%	$236.5119	$236.51	$236.50	$236.50
Purchase #7	$241.69	4.688%	$253.0204	$253.02	$253.00	$253.00
7 purchase totals =	$927.99		$1,013.1109	$1,013.11	$1,013.00	$1,013.10