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	$103.92	13.787%	$118.2475	$118.25	$118.25	$118.20
Purchase #2	$239.88	7.842%	$258.6914	$258.69	$258.70	$258.70
Purchase #3	$226.75	12.724%	$255.6017	$255.60	$255.60	$255.60
Purchase #4	$80.47	10.614%	$89.0111	$89.01	$89.00	$89.00
Purchase #5	$110.85	4.401%	$115.7285	$115.73	$115.75	$115.70
Purchase #6	$127.54	4.180%	$132.8712	$132.87	$132.85	$132.90
Purchase #7	$62.65	8.386%	$67.9038	$67.90	$67.90	$67.90
7 purchase totals =	$952.06		$1,038.0552	$1,038.05	$1,038.05	$1,038.00